Objective:To explore the effect of complement depleting with cobra venom factor(CVF) on apoptosis of glomerular mesangial cells(GMCs) and expression of growth arrest and DNA damage inducible protein 45 α(Gadd45α) in rats with Thy-1 nephritis(Thy-1 N). Methods:The rat model of Thy-1 N was reproduced with rabbit anti-thymocyte serum(ATS). The rats were divided into 3 groups, control group,Thy-1 N group and CVF+Thy-1 N group. The complement hemolytic activity(CH50) was determined by red cell hemolytic test. Apoptosis in GMCs was examined by electron microscope(EM) and Tdt-mediated X-dUTP nick end labeling(TUNEL). The mRNA of Gadd45α was measured by RT-PCR and real-time PCR at 40 min,3,6,12 and 24 h, meanwhile the expression of Gadd45α protein was determined by Western blot at 3 h. Results:CH50 activity in CVF+Thy-1 N group at 40 min,3,6,12,24 h and 5 d was significantly lower than that in Thy-1 N group and control group(P < 0.01). In Thy-1 N group, some GMCs began to undergo apoptosis at 40 min, more prominent at 3 h, and decreased gradually. But, in CVF+Thy-1 N group, the number of apoptosis cells was markedly less than that in Thy-1 N group at above-mentioned time. The expression of Gadd45α gene from renal tissues in Thy-1 N group was up-regulated at 40 min, reached peak level at 3 h, but the expression level of Gadd45α mRNA in CVF+Thy-1 N group was significantly less than that in Thy-1 N group(P < 0.01). The expression of Gadd45α protein in Thy-1 N group was higher than that in control group at 3 h, but the protein expression in CVF+Thy-1 N group was markedly less than that in Thy-1 N group(P < 0.01). Conclusion:Complement depleting with CVF could obviously decrease the apoptosis of GMCs and inhibit the expression of Gadd45α gene in rats with Thy-1 nephritis.