History and Objectives: Hypertension is one of the common diseases with complications that lead to death. Some researches has argued that in patients with hypertension, the level of C3 in serum is elevated. This study was carried out to determine the level of C3 in patients with hypertension and to compare it with control group in Isfahan province in 1998.

Materials and Methods: The analytical strategy of this study was randomly performed on 60 patients with hypertension and on 60 normal persons. The SRID method was used to determine the level of C3 in serum. Both groups were similar regarding age and gender. For statistical analysis t-test was used.

Results: C3 level was 85±13 in normal persons and 131±32 mg/dl in patients with hypertension with a 54% difference (P<0.0001). In addition, its level showed no relationship with gender. In patients with hypertension, there was a lower increase in the level of C3 with age.

Conclusion: Hypertension can increase the level of C3 in serum. It is recommended to carry out a cohort research study for finding a relationship between an increase in the level of C3 in patients with hypertension and incidence of atherosclerosis.