The kinetics of PhEt oxidn. with an O-3-air mixt. in glacial AcOH in presence of Mn(OAc)(2) was studied. Introduction of the catalyst resulted in an increase of the side-chain oxidn. selectivity from 34.0 to 83.7%. AcPh (76.0%) and PhMeCHOAc (9.7%) were the main reaction products. Traces of PhMeCHOH and PhCHO were found in the reaction mixt. No products of PhH ring ozonolysis were detected.