Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly population. Evidence has shown that the human immune system may play critical roles in this disease. Inducible costimulator (ICOS) promotes T-cell activation, differentiation, and T:B-cell interactions. The aim of the study was to understand the effect of ICOS on the development of AMD from genetic polymorphism perspective and serum level perspective. Two ICOS polymorphisms, rs10183087A/C and rs10932037C/T, were tested in 223 AMD cases and 262 healthy controls. The serum level of soluble ICOS (sICOS) was compared among subjects with different genotypes, as well as between AMD patients and controls. Data showed that prevalence of rs10183087CC genotype was significantly increased in AMD than in controls (p=0.001). Function analysis revealed that subjects carrying rs10183087CC genotype had higher serum levels of sICOS than those with AA or AC genotypes (p<0.05). When we compared serum levels of sICOS between cases and controls, results showed that AMD patients had significantly increased sICOS levels than healthy donors (p<0.05). Also, wet type cases were observed to have higher sICOS levels than cases with dry type (p<0.05). These data suggested ICOS polymorphism could affect the susceptibility to AMD by elevating protein expression, and serum levels of sICOS may be closed correlated with the development and progression of this disease.