The present study assessed the urinary protein with SDS-PAGE technique and by using gentamicin as a positive control for a comparative study to evaluate the renal toxic effect of gossypol. Results indicated that gentamicin could induce proteinuria by alteration of glomerular permeability to cause over-filtration of high molecular weight proteins, damage the brush border (BB) membrane of proximal renal tubules and impair tubular reabsorption function. Gossypol could also induce proteinuria in certain cases of guinea pigs but not at all in gossypol-treated rats. However, an increase in low molecular weight protein bands (M.W. range 20-30 kd) in urinary electrophoregram of gossypol-treated rats were detectable.