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Leaf curl, caused by Taphrina deformans, is a serious disease on peaches and nectarines. Heavily infected fruit trees are poorly nourished, develop fewer flower buds, and are more easily damaged from freezing in winter. To prevent these negative effects, the best approach is to breed and grow cultivars genetically resistant to the pathogen.In this research,susceptibility of 82 peach and 22 nectarine varieties to leaf curl disease was investigated in ecological conditions of Isparta province in 2003 and 2004. Disease severity was calculated by the 0-5 scale when typical symptoms of leaf curl were evaluated on peach and nectarine leaves in naturally infected orchards.The conditions of natural infection allowed grouping the biological material in 4 classes (plant growth stages) and 6 groups of resistance for leaf curl disease severity. The results indicated that early varieties; ‘Sun High and Tejon’, middle early variety; ‘Flour Dasun’, middle season variety; ‘Shesta’ and late varieties; ‘Andros, Muir and Red King’ were determined as highly susceptible. All of the early nectarine varieties, middle early varieties; ‘Crimson Cold, Independence and Spring Red’, middle season varieties; ‘Nec8, Stark Red Gold and Nec-6’ and late variety ‘June Berta’ were found as susceptible varieties