Protein fouling is one of the critical factors governing the effectiveness of many microfiltration processes. Although mechanisms have been proposed, direct correlation between protein amount fouled on membranes and filtration behavior is required. We developed a simple method to measure proteins on microfiltration membranes. The protein-fouled membranes were stained by amido black 10B first, then destained to remove excess dye not bound to protein. Finally, the dye associated with the protein on the membranes was eluted with 0.1 N NaOH. Three membranes (mixed esters of cellulose nitrate and acetate membrane, Durapore GVWP membrane, and. nuclear-pore membrane) were examined by blotting, adsorbing, and depositing bovine serum albumin on them. The absorbency of the eluted solutions was measured at 620 nm. The absorbency of the eluted solutions was independent of staining time and eluting time, but decreased with prolonged destaining time. The results showed a good linear relationship between the absorbency and amount of protein on membranes in all conditions examined. Three other proteins were also examined and the results showed that different proteins have different slopes. These results indicate that the method could be used to quantify proteins fouled on membrane.