diff --git a/README.md b/README.md
index 394a4f4..2209b5d 100644
--- a/README.md
+++ b/README.md
@@ -163,6 +163,7 @@ At this time, support for the following ontologies is tested:
 * Human Phenotype Ontology (HPO)
 * Gene Ontology (GO)
 * Medical Action Ontology (MAxO)
+* Units of Measurement Ontology (UO)
 
 Other ontologies are very likely to work too.
 In case of any problems, please let us know on our [Issue tracker](https://github.com/P2GX/ontolius/issues).
diff --git a/resources/uo/uo.json.gz b/resources/uo/uo.json.gz
new file mode 100644
index 0000000..72c3233
Binary files /dev/null and b/resources/uo/uo.json.gz differ
diff --git a/src/common.rs b/src/common.rs
index 090359a..267f1dd 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -41,6 +41,16 @@ pub mod maxo {
     pub static MEDICAL_ACTION: TermId = make_term_id(KnownPrefix::MAXO, 1, 7);
 }
 
+/// Constants for working with Unit of Measurement Ontology (UO).
+pub mod uo {
+    use crate::{term_id::KnownPrefix, TermId};
+
+    use super::make_term_id;
+    /// [unit (UO:0000000)](http://purl.obolibrary.org/obo/UO_0000000)
+    /// is the root of all terms in the UO.
+    pub static UNIT: TermId = make_term_id(KnownPrefix::UO, 0, 7);
+}
+
 /// Constants for working with Gene Ontology (GO).
 pub mod go {
     use crate::{term_id::KnownPrefix, TermId};
diff --git a/src/term_id.rs b/src/term_id.rs
index acfd679..a9efa40 100644
--- a/src/term_id.rs
+++ b/src/term_id.rs
@@ -459,6 +459,7 @@ pub(crate) enum KnownPrefix {
     CHEBI,
     NCIT,
     PMID,
+    UO,
 }
 
 impl PartialEq<str> for KnownPrefix {
@@ -475,6 +476,7 @@ impl PartialEq<str> for KnownPrefix {
             KnownPrefix::CHEBI => other == "CHEBI",
             KnownPrefix::NCIT => other == "NCIT",
             KnownPrefix::PMID => other == "PMID",
+            KnownPrefix::UO => other == "UO",
         }
     }
 }
@@ -493,6 +495,7 @@ impl Display for KnownPrefix {
             KnownPrefix::CHEBI => f.write_str("CHEBI"),
             KnownPrefix::NCIT => f.write_str("NCIT"),
             KnownPrefix::PMID => f.write_str("PMID"),
+            KnownPrefix::UO => f.write_str("UO"),
         }
     }
 }
@@ -525,7 +528,9 @@ impl TryFrom<&str> for KnownPrefix {
             Ok(KnownPrefix::NCIT)
         } else if value.starts_with("PMID") {
             Ok(KnownPrefix::PMID)
-        } else {
+        } else if value.starts_with("UO") {
+            Ok(KnownPrefix::UO)
+        }else {
             Err(())
         }
     }
diff --git a/tests/test_common.rs b/tests/test_common.rs
index 05b83dc..e52ae44 100644
--- a/tests/test_common.rs
+++ b/tests/test_common.rs
@@ -1,4 +1,4 @@
-use ontolius::common::{go, hpo, maxo};
+use ontolius::common::{hpo, go, maxo, uo};
 
 #[test]
 fn hpo_commons_are_accessible() {
@@ -18,3 +18,10 @@ fn go_commons_are_accessible() {
 fn maxo_commons_are_accessible() {
     assert_eq!(maxo::MEDICAL_ACTION, ("MAXO", "0000001"))
 }
+
+#[test]
+fn uo_commons_are_accessible() {
+    assert_eq!(uo::UNIT, ("UO", "0000000"))
+}
+
+
diff --git a/tests/test_io.rs b/tests/test_io.rs
index 29d4eb8..985f853 100644
--- a/tests/test_io.rs
+++ b/tests/test_io.rs
@@ -364,3 +364,82 @@ mod medical_action_ontology {
         _ = maxo.version();
     }
 }
+
+
+/// Unit of Measurement Ontology (UO) tests.
+mod unit_measurement_ontology {
+
+    use std::fs::File;
+    use std::io::BufReader;
+    use std::sync::OnceLock;
+
+    use flate2::bufread::GzDecoder;
+    use ontolius::common::uo::UNIT;
+    use ontolius::io::OntologyLoaderBuilder;
+    use ontolius::ontology::csr::MinimalCsrOntology;
+    use ontolius::ontology::{HierarchyWalks, MetadataAware, OntologyTerms};
+    use ontolius::term::MinimalTerm;
+    use ontolius::TermId;
+
+    const UO_PATH: &str = "resources/uo/uo.json.gz";
+
+    fn uo() -> &'static MinimalCsrOntology {
+        static ONTOLOGY: OnceLock<MinimalCsrOntology> = OnceLock::new();
+        ONTOLOGY.get_or_init(|| {
+            let reader = GzDecoder::new(BufReader::new(
+                File::open(UO_PATH).expect("Obographs JSON file should exist"),
+            ));
+            let loader = OntologyLoaderBuilder::new().obographs_parser().build();
+            loader.load_from_read(reader).expect("Obographs JSON should be well formatted")
+        })
+    }
+
+    macro_rules! test_ancestors {
+        ($($ontology: expr, $curie: expr, $expected: expr)*) => {
+            $(
+                let query: TermId = $curie.parse().unwrap();
+
+                let mut names: Vec<_> = $ontology
+                    .iter_ancestor_ids(&query)
+                    .map(|tid| $ontology.term_by_id(tid).map(MinimalTerm::name).unwrap())
+                    .collect();
+                names.sort();
+                assert_eq!(
+                    names,
+                    $expected,
+                );
+            )*
+        };
+    }
+
+    #[test]
+    fn iter_ancestor_ids() {
+        let uo = uo();
+
+        test_ancestors!(
+            uo,
+            "UO:0010002", // millisiemens
+            &["conduction unit", "electrical conduction unit", "siemens based unit", "unit"]
+        );
+        test_ancestors!(
+            uo,
+            "UO:0000010", // second
+            &["base unit", "second based unit", "time unit", "unit"]
+        );
+    }
+
+    #[test]
+    fn we_get_expected_descendant_counts_for_uo_root() {
+        let uo = uo();
+
+        let descendant_count = uo.iter_descendant_ids(&UNIT).count();
+        assert_eq!(descendant_count, 549);
+    }
+
+    #[test]
+    fn version_parsing() {
+        let uo = uo();
+
+        assert_eq!(uo.version(), "2026-01-09") ;
+    }
+}
\ No newline at end of file