1) The prevention of hydrolysis of ester, using methantheline bromide (Banthine) as an example, with surfactants was examined. Surfactants used were anionic, cationic, and nonionic. Anionic surfactant (sodium laurylsulfate) markedly prevented the hydrolysis (the half life becomes 100 times longer in 0.5% laurylsulfate solution) and nonionic surfactant prevents it slightly. 2) Hydrolysis in sodium laurylsulfate solution does not follow a pseudo-first order course and is influenced by a buffer concentration. 3) The higher the concentration of sodium laurylsulfate, the slower became the hydrolysis.