Objective To observe the distribution and number of mast cells in the renal tissues of patients with membranous nephropathy at different pathological stages and to investigate the pathological significance of mast cells. Methods Renal tissue samples from 55 membranous nephropathy patients of different pathological stages with available full clinical and pathological data and from 8 normal kidney donors were collected in this study. The number and distribution of mast cells in each tissue section was observed by immunochemical staining for the cell specific marker C3aR. Then the mast cell density in the cortex was calculated. The correlation of mast cells with patients’ clinical and pathological indices was analyzed. Results Mast cells were mainly distributed in the tubular interstitial area, especially in the area with injured tubules and glomeruli. There were more renal mast cells in the patients with membranous nephropathy of all pathological types when compared with the normal controls. No significant difference in the number of renal mast cells was found between the groups of different pathological stages except stage Ⅰ group having less cells. The number of renal mast cells was correlated with indices reflecting renal injury, especially with the indices reflecting renal tubular and interstitial injury. Conclusion Our results indicate that mast cells are involved in the pathogenesis of membranous nephropathy, especially in the chronic tubular interstitial injury. As a possible new pathogenic factor and a new therapeutic target, renal mast cells deserve attention in the treatment of membranous nephropathy.