Abstract： Objective To explore the association between complement C3 and the prevalence of simple fatty liver disease and nonalcoholic steatohepatitis. Methods A total of 2 799 health check-up participants were recruited from Tianjin Medical University General Hospital-Health Management Centre. Serum C3 levels were measured using immunoturbidimetry method and simple fatty liver disease and nonalcoholic steatohepatitis were diagnosed by liver ultrasonography and serum alanine aminotransferase concentration. Multiple logistic regression analysis was used to examine the association between quartiles of serum C3 levels and the prevalence of simple fatty liver disease and nonalcoholic steatohepatitis. Results After adjusting for covariates, the odds ratios (95% confidence interval) of simple fatty liver disease and nonalcoholic steatohepatitis for increasing quartiles of C3 were: 1.00 (reference), 2.15 (1.55, 3.01), 3.28 (2.35, 4.6) and 4.31 (3.11, 6.02); and 1.00 (reference), 4.54 (1.68, 15.91), 7.81 (3.02, 26.67) and 14.91 (5.94, 50.14) (both P for trend<0.000 1), respectively. Conclusions The study found that the elevated C3 levels were significantly associated with the prevalence of simple fatty liver disease and nonalcoholic steatohepatitis. Further study is needed to clarify whether C3 has a predictive value for the occurrence of nonalcoholic fatty liver disease.