The kinetics of the degradation of cinnarizine [a cerebral blood flow improver] in aqueous solution at various pH values and 4 different temperatures were investigated. The degradation of cinnarizine was observed as a pseudo first-order reaction. Determining the degradation rate of cinnarizine at various pH values showed that the degradation rate of cinnarizine increased with decreasing pH within the range from pH 3.0 to 1.0. The rate remained unchanged at < pH 1.2, and cinnarizine was stable at > pH 3.0. The pseudo first-order rate constants in aqueous solution (pH 1.20) at 60, 70, 80 and 90.degree. C were 1.85 .times. 10-5, 1.05 .times. 10-4, 4.07 .times. 10-4 and 1.94 .times. 10-4/min, respectively. The activation energy of degradation in aqueous solution (pH 1.20) was 36.8 kcal/mol from an Arrhenius plot.