OBJECTIVE:To discuss the association between ABCB1 gene polymorphisms and adriamycin and cyclophospha-mide(AC)combined with chemotherapy-induced severe neutropenia in patients with breast cancer. METHODS:218 breast cancer patients receiving AC combined with chemotherapy were selected from our hospital during 2012-2015;PCR-RFLP was used to de-tect polymorphisms of ABCB1 2677G>T/A and 3435C>T. The associated between different age,BMI,clinical stages genotypes, etc and AC combined with chemotherapy-induced severe neutropenia were investigated,and risk factors of neutropenia were ana-lyzed by multivariate logistic regression. RESULTS:Among 218 breast cancer patients,170 patients suffered from severe neutrope-nia,accounting for 78.0%. Among ABCB1 2677G>T/A polymorphisms,distribution frequency of GT or GA genotype,TT,TA or AA genotype,GG genotype in severe neutropenia were 80.6%,86.2% and 60.0%,with statistical significance (P<0.05). Among ABCB1 3435C>T polymorphisms,distribution frequency of TT,CT and CC genotype in severe neutropenia were 86.4%, 78.4% and 72.7%,there was no statistical significance(P>0.05). AST and ABCB1 2677G>T/A polymorphisms were correlated with severe neutropenia (P<0.05),and ABCB1 2677G>T/A polymorphism was a strong predictor of neutropenia [OR=3.875, 95%CI(1.555,9.922),P=0.008]. CONCLUSIONS:ABCB1 2677>T/A polymorphisms may be aggravate AC combined with che-motherapy-induced neutropenia in patients with breast cancer.