Abstract: In this paper, it is shown that a c oscillopolarographic titration can be applied advantageously to titrate neostigmine methyl sulfate by sodium tetraphenylborate(NaTPB).NaTPB is added to precipitate quantitatively, neostigmine methyl sulfate from aqueous solution. Filter part of the mixture, and the excess of NaTPB in the filtrate is titrated by thallous sulfate standard solution, using the disappearance of the incision of NaTPB on dE/dt—E curve to indicate the end point of titrations. The recovery was 99.3～100.2%. Ten determinations on the same samplegave a relative standard deviation of ±0.42%. The method is accurate, rapid and Simple, much superior to the official method adopted now.