It was a single-center cross-sectional study to investigate the association of serum C3 level with blood pressure and estimated glomerular filtration rate (eGFR) in patients with idiopathic membranous nephropathy (IMN). The clinical and pathological data of 98 patients with IMN diagnosed by renal biopsy in the Department of Nephrology of East Hospital Affiliated to Tongji University from August 1, 2018 to October 31, 2023 were retrospectively analyzed. The demographic characteristics, serum complement C3 and other clinical data were compared between the non-hypertension group ( n=37) and hypertension group ( n=61). Pearson or Spearman correlation analysis method was used to analyze the correlation between serum C3 and eGFR in IMN patients and IMN patients with hypertension. Multiple linear regression analysis was used to analyze the related factors of eGFR in IMN patients with chronic kidney disease stage 1-3 in hypertension group. The results showed that compared with the non-hypertension group, the patients in hypertension group were older, and had higher levels of serum creatinine, cystatin C, urinary microalbumin to creatinine ratio, serum C3 and C4, and lower eGFR (all P<0.05). The correlation analysis showed that there was no correlation between serum C3 level and eGFR in IMN patients ( r=0.118, P=0.247). However, serum C3 level was positively correlated with eGFR in IMN patients with hypertension ( r=0.325, P=0.011). Multiple linear regression analysis showed that eGFR was negatively correlated with age ( β=-0.328, P=0.013), and positively correlated with serum C3 level ( β=0.228, P=0.048). The study shows that serum C3 level in hypertension group is higher than that in non-hypertension group in IMN patients. Moreover, serum C3 is positively correlated with eGFR.