AIM: To obtain active human recombinant uridine diphosphate glucuronosyltransferase 1A3(UGT1A3) enzyme from Chinese hamster lung (CHL) cells.METHODS: The full-length UGT1A3 gene was amplified by reverse wanscription-polymerasechain reaction (RT-PCR) using total RNA from human liver as template. The correct fragmentconfirmed by sequencing was subcloned into the mammalian expression vector pcDNA3.1 (+),and recombinant vector was transfected into CHL ceils using a calcium phosphate method.Expressed UGT1A3 protein was prepared from CHL cells resistant to neomycin (G418). Then theprotein was added into a reaction mixture for glucuronidation of quercetin. The glucuronidationactivity of UGT1A3 was determined by reverse phase-high performance liquid chromatography(RP-HPLC) coupled with diode array detector (DAD). The quercetin glucuronide was confirmedby hydrolysis with β-glucuronidase. Control experiments were performed in parallel. Thetranscription of the recombinant was also determined by RT-PCR.RESULTS: The gene was confirmed by DNA sequencing, and it was an allele (UGT1A3-3) ofUGT1A3. The fragment was introduced into pcDNA3.1 (+) successfully. Several colonies wereobtained under the selection pressure of G418. The result of RT-PCR showed transcription ofrecombinants in mRNA level. Glucuronidation assay and HPLC analysis indicated UGT1A3expressed heterologously in CHL cells was in an active form, and one of gulcuronidescorresponding to quercetin was also detected.