Levels of protein carbonylation in peach fruits inoculated with four antagonistic yeasts (Pichia membranaefaciens, Cryptococcus laurentii, Candida guilliermondii and Rhodotorula glutinis) were significantly reduced in response to reactive oxygen species (ROS) caused by Monilinia fructicola. In control fruit without yeast treatments, proteins carbonylation obviously increased after inoculation with M. fructicola, ranging from molecular mass 20 to 120 kDa. However, in yeast-treated fruits, no proteins carbonylation was detected at 1 d, only a small quantity of carbonylation ranging from 28.5 to 45 kDa was found at 2 d. Antagonistic yeasts significantly stimulated the activities of chitinase, beta-1,3-glucanase, catalase (CAT), peroxidase (POD) and the expressions of relevant genes during all storage periods. These results suggest that yeast treatments may be related to alleviating proteins carbonylation and mitigating pathogen-induced oxidative damage, which result in decrease of fruit decay and imply that antioxidant defense response may be involved in the mechanisms of microbial biocontrol agents against fungal pathogen. (C) 2008 Elsevier B.V. All rights reserved.