Aim To observe the regularity of fluctuation of serum C-reactive protein (CRP) level in patients with acute cerebral infarction (ACI) and to investigate the relationship between the serum CRP level and the development and prognosis of ACI, and its clinical significance. Methods The serum CRP level was determined serially (on day 1, 7 and 14 after onsets) by immune turbidity method in 66 patients with ACI and 45 normal controls. Results In ACI group, the serum CRP level increased on first day was significantly (p<0.01) higher than that in the controls, showing a highest serum CRP level in severe patients. It reached the peak on seventh day and then tended to decrease gradually. Conclusions This study suggests that high serum CRP level may play a role in the development of ACI, and serum CRP level is positivly correlated with severity extent of ACI.