273 chinese have been studied with high voltage electrophoresis and immumofixation to survey the polymorphism of the third component of human complement in Shaanxi Provice Two C_3 phenotypes were found in this population, they are C_3SS and C_3FS The frequencies of C_3SS and C_3FS are 98.53% and 1.47% respectively. The frequency of C_3S gene is 0.9926 and C_3F gene 0.0073. These results are similar to other studies in China and this group was in Hardy-Weinberg equilibrium. Compared with Negro and Caucasian, the chinese population in Shaanxi Province has a significant difference in C_3 polymorphism.