Abstract: In order to provide valuable information for the establishment of the determination and pre-treatment methods of otilonium bromide in different samples，the stability and degradation products of otilonium bromide in different media were studied，and the degradation characteristics of otilonium bromide in these media were also investigated.The stability of otilonium bromide in alcohols，water，acetonitrile and plasma was investigated by HPLC；the degradation products were identified by LC-MS/MS，^1H NMR and ¹³C NMR.Test results showed that otilonium bromide readily undergoes alcoholysis，hydrolysis,and enzymolysis in plasma at room temperature.It was converted into p-［2-(n-octyoxy)benzoyl］-aminobenzoic acid methyl ester and diethyl-(2-hydroxyethyl)-methyl ammonium bromide in methanol，and undergoes hydrolysis or enzymolysis to yield the degradation products p-［2-(n-octyoxy)benzoyl］-aminobenzoic acid and diethyl-(2-hydroxyethyl)-methyl ammonium bromide in water and plasma.No degradation of otilonium was found in acetonitrile.Otilonium bromide was unstable in methanol，ethanol，water and plasma at room temperature，but stable in acetonitrile.Thus，alcohols and water should be avoided as the solvent of otilonium bromide when establishing the analytical methods.Acetonitrile is suggested to be a suitable solvent for otilonium bromide.The rapid degradation of otilonium bromide in plasma can be prevented by immediate addition of potassium fluoride(an inhibitor of plasma esterase) to the freshly collected plasma before prompt treatment with acetonitrile.