In this study, we analyzed five potentially functional SNPs in ICOS gene, including rs11889031C/T in promotor, rs10932029 C/T and rs4675374C/T in the intron1, rs10183087A/C and rs10932037 C/T in the 3'-untranslating region (UTR), and determine their associations with breast cancer. The gene discussed is ICOS; the disease is breast cancer.