The erythrocyte complement receptor 1 (ECR1) activity and CR1 quantitative genotype distribution were studied and the mechanisms of decreased ECR1 activity in cerebral infarction revealed. By using red blood cell yeast rosette test ECR1 activities were measured and by using PCR-RFLP CR1 Hind Ⅲ genomic polymorphism detected in the patients with cerebral infarction and healthy controls. The results showed that the level of C3bRR was decreased and the level of CICRR increased in the patients with cerebral infarction as compared with healthy controls (both P<0.05). CR1 quantitative genotype distribution in the patients with cerebral infarction was differed significantly from that of healthy controls (P<0.05). It was concluded that the decrease of ECR1 activity in the patients with cerebral infarction was correlated with CR1 Hind Ⅲ genomic polymorphism.