Abstract: Objective To investigate uridine diphosphate glucuronosyltransferase（UGT） 1A1 gene polymorphism as the predictor of safety and efficacy of FOLFIRI regimen as secondline treatment in metastatic colorectal cancer（mCRC） patients. MethodsPeripheral blood mononuclear cells form the mCRC patients were separated before FOLFIRI chemotherapy and the UGT1A1 genotypes were determined by the fluorescence quantitative PCRHRM method. The side effects and tumor response were evaluated using NCICTC 30 and RECIST 10 criterion, respectively. The correlation between UGT1A1 gene polymorphisms and side effects or objective response rate（ORR） was subsequently analyzed. Progression free survival（PFS） was recorded and survival analysis was carried out by KaplanMeier method for the impact of genotypes on PFS. Results The UGT1A1 genotypes in 38 consecutive patients were as follows：UGT1A1*28 homozygous wildtype TA6／6（31 cases， 81.6％）， heterozygous mutanttype TA6／7（2 cases， 5.3％）， homozygous mutant type TA7／7（5 cases， 13.2％）； UGT1A1*6 wild type G／G（28 cases， 737％）， heterozygous mutanttype G／A（8 cases， 21.1％）， homozygous mutant type A／A（2 cases， 5.3％）. For the incidence rate of grade 3 to 4 delayed diarrhea and neutropenia，the rates were significantly lower in patients of UGT1A1*28 TA6／6 widetype genotype than those of TA6／7 and TA7／7 mutanttype genotypes（P＜0.05）. The rate was significantly lower in patients of UGT1A1*6 G/G genotype than that of G／A and A／A mutanttype genotypes（P＜0.05）. No significant difference of either ORR or PFS was observed among different genotypes（P＞0.05）. Conclusion For FOLFIRI regimen as second-line chemotherapy in mCRC patients， the UGT1A1*28 and UGT1A1*6 locus mutations can be regarded as predictors for irinotecanassociated severe delayed diarrhea and neutropenia， whereas no association between UGT1A1 gene polymorphism and efficacy is observed.