Abstract: OBJECTIVE To investigate UGT1A1 gene polymorphism and adverse relevance of irinotecan users in Taizhou, Zhejiang. METHODS Choose 132 Han nationality tumor patients treated with irinotecan-based chemotherapy in Taizhou. Take their peripheral blood to extract DNA for test of UGT1A1 gene polymorphism. RESULTS Among 132 cancer patients in Taizhou collected to detect UGT1A1 gene polymorphisms, the rates of wide type TA (6/6), heterozygous mutants TA(6/7), homozygous mutants TA(7/7) of UGT1A1*28 gene were 70.45%, 27.27%, 2.27%. The rates of UGT1A1*6 wide type G/G were 73.48% and heterozygous mutants of G/A were 26.52%. The incidence of diarrhea in UGT1A1*28 non-wild type patients (6/7+7/7) was significantly higher than that in wild type patients (P=0.040). There was no significant difference between UGT1A1*28 gene polymorphism and neutropenia, thrombocytopenia and hemoglobin reduction. There was no correlation between UGT1A1*6 gene polymorphism and delayed diarrhea, neutropenia, thrombocytopenia and hemoglobin reduction. CONCLUSION UGT1A1 has a high frequency in Taizhou, Zhejiang. To TA(6/7) and TA(7/7) throng, there are obviously more diarrhea after using irinotecan during TA(6/6) wild-type throng. The study suggests that lung and colorectal cancer patients in Taizhou, Zhejiang, should do the test of UGT1A1 gene promoter polymorphism before chemotherapy with irinotecan. It will assist predicting patients' resistance so that it can adjust the dosage to help the smooth progress of chemotherapy.