Objective To investigate the effects of treatment with norcantharidin(NCTD) on proteinuria and renal pathology in protein-overload nephropathy rats. Methods Uninephrectomized SD rats received intraperitoneally injections of bovine serum albumin (BSA). The nephropathy rats were randomly divided into model group(BSA by intraperitoneally injection ) and NCTD group(BSA and NCTD 0.1 mg·kg-1·d-1 by intraperitoneally injection). An additional set of uninephrectomized rats only received saline as control group. Each group consisted of 8 rats. Twenty-four-hour urinary protein was measured weekly. At the end of the fifth week, the rats were sacrificed after anticoagulant blood and serum were collected and the remnant kidney of each rat was harvested and weighed for the examination of light microscopy, electron microscopy and immunofluorescence staining. Results Compared with control group, the ratio of kidney weight/body weight, urinary protein excretion, average score of glomerulosclerosis and tubulointerstitial lesion increased significantly(P < 0.01), but serum albumin(Alb) decreased obviously (P < 0.01)in model group. Electron microscope showed that mesangium region enlarged with obvious electron dense deposits, and foot process fusion was seen extensively in model group. Immunofluorescence of IgG and C3 with the intensity of 3+~4+ was also found in mesangium region of model group. After intervention with NCTD, the above-mentioned parameters, except that Alb enhanced significantly(P <0.01), all decreased significantly(P < 0.05 or 0.01). In NCTD group, few electron dense deposits and local foot process fusion were found, while immunofluorescence staining intensity of IgG and C3 weakened. There were no significant differences of serum creatinine(Scr), BUN and blood routine among all groups(P > 0.05). Conclusion NCTD may decrease the proteinuria of protein-overload nephropathy rats and attenuate tubulointerstitial lesion without severe side effects of liver, kidney or bone marrow.