A kinetic spectrophotometric method has been developed for the determination of acetylsalicylic acid (ASA) in model sоlutions and dosage form "ACELYSIN-KMP". The proposed procedure is based on the indicator reaction of catalytic p-phenetidine oxidation by hydrogen peroxide in a weak alkaline medium. Compresent components and potential hydrolytic cleavage products do not interfere the ASA determination. Calibration graph for ASA has linear dependence in the range 12 - 180 μmol L-1. The limit of quantitation is 12 μmol L-1. For five determinations of 44 μmol L-1, 88 μmol L-1 and 130 μmol L-1 ASA the reproducibility has a RSD of 1.18, 1.06 and 0.76% respectively. Hence the proposed method is more sensitive, simple and express in comparance with the well-known one. Dosage form "ACELYSIN-KMP" recovery is 98.95 ± 1.32% of ASA.