OBJECTIVE： To study the correlation of UGT1A1 gene polymorphisms with the incidence and severity of irinotecan-associated ADR in the patients with irinotecan-based chemotherapy. METHODS： 56 patients with advanced gastroenteric tumor and small cell lung carcinoma were selected from our hospital and treated with irinotecan-based chemotherapy. The occurrence of ADR was observed during chemotherapy. Gene DNA were collected from peripheral blood sample， and UGT1A1 gene polymorphisms was determined. The relationship of genotypes with ADR was analyzed. RESULTS： TA sequence of UGT1A1*28 genetic locus was as follows：  wild-type genotype TA6/6 （42 cases， 75.0％）， heterozygous mutation-type TA6/7 （13 cases， 23.2％） and homozygous mutation-type TA7/7 （1 cases， 1.8％）； that of UGT1A1*6 genetic locus was as follows： wild-type genotype （44 cases， 78.6％）， heterozygous mutation-type （10 cases， 17.9％） and homozygous mutation-type （2 cases， 3.6％）. In UGT1A1*28 genetic locus， 6 wild-type genotype patients and 3 mutation-type patients suffered from Ⅲ degree or above hypoleukemia and/or neutropenia （14.3％ vs. 21.4％，P＞0.01）， among which only one homozygous mutation-type patient suffered from hypoleukemia and/or neutropenia （100％）； 6 wild-type genotype patients and 2 mutation-type patients suffered from Ⅲ degree or above diarrhea （14.3％ vs. 14.3％， P＞0.01）， among which only one homozygous mutation-type patient suffered from Ⅲ degree or above diarrhea （100％）. In UGT1A1*6 genetic locus， 3 wild-type genotype patients and 8 mutation-type patients suffered from Ⅲ degree or above neutropenia （6.8％ vs. 66.6％，P＜0.01）， and 2 wild-type genotype patients and 7 mutation-type patients suffered from Ⅲ degree or above diarrhea （4.5％ vs. 58.3％，P＜0.01）. CONCLUSIONS： Among patients with advanced gastroenteric tumor and small cell lung carcinoma， UGT1A1 gene wild-type gene promoter is most common， followed by heterozygous mutation-type， and homozygous mutant rare. For TA7/7 homozygous mutation-type patients， irinotecan-based chemotherapy increase the risk of Ⅲ degree or above hypoleukemia and/or neutropenia and diarrhea. For TA6/7 heterozygotes patients and TA6/6 wild-type patients， irinotecan-based chemotherapy doesn’t affect the incidence of Ⅲ degree or above neutropenia and diarrhea. For UGT1A1*6 genetic locus mutation-type patients， irinotecan-based chemotherapy significantly increase the risk of Ⅲ degree or above neutropenia and diarrhea.