Isoates with changed pathogenicity were selected among iprodione-resistant Alternaria mali to investigate any relationship between their pectolytie enzyme activity and pathogenicity. In artificial medium, strongly pathogenic isolates $S_1$, and $R_3$ showed higher enzyme activity than weakly pathogenic isolate $R_8$.Activity of endo-polymethylgalacturonase and end-o-polygalacturonase was more than 3 times. But activity of pectin methylesterase and pectin Iyase by isolaste $S_1$ was higher than those by $R_3$ and $R_8$ isolates. In apple medium dialyzed against distilled water, activity of enzyme by each isolate was increased but growth of each isolate was reduced. When iprodione was added to the medium, enzyme activity and growth of isolate $S_1$, were reduced but strongly pathogenic isolate .$R_3$ among iprodione-resistant ones showed increased enzyme activity except for exo-polygalacturonase in dialyzed apple medium.