Abstract: The covalent attached self assembled film based on bovine serum albumin (BSA) and diazoresin (DR) irradiated by UV for 10min has negative electric charges after it was immersed into a pH=3 0 or pH=9 0 solution for 10min because the disulfide bonds in the protein are liable to decomposition. Methylene blue (MB) was absorbed on the surface of the DR/BSA self assembled film. The amount of MB absorption on the film treated by acid solution was much higher than that treated by base solution. At the same time, the desorption of MB in acid was much faster than that in base. The DR/BSA self assembly film might hopefully act as probes for cations in the future.