In this study, serum complement protein (C3 and C4) levels were investigated among 19 patients with type 1 diabetes mellitus and 15 healthy subjects who admitted to the clinic of internal disease of Medical Faculty at Cumhuriyet University. The levels of C3 and C4 among the diabetic patients were found as follows: C3 = 108.6 ± 7.4 lU/ml, C4 = 90.89+6.6 IUlml. Complement components (C3 and C4) were not significantly different compared to the controls (p>0.05). The levels of C3 and C4 in diabetic patients with or without complications were as follows: C3 = 10.75 ± 8.7 IUlml, C4 = 83.6 ±8.2 IUlml and C3 = 113.1 ±5.8 IUlml, C4 = 96.27 ±9.7 IUlml, respectively. The differences in respect of C3 and C4 level between the groups were not significant (p>0.05). Also, when the influence of duration of diabetes on complement levels are investigated, the duration of disease was found to have no significant effects on the complement levels (p>0.05).