Various rice cultivars were selected and screened for their reaction to sheath blight in the greenhouse. Cluster analysis of percent relative lesion height (% RLH) generated four groups of cultivars with a coefficient of similarity of 3.27. Chitinase activities were detected 24 h after inoculation of moderately resistant cvs Betichikon, Dudruchi, Khatochalani, Padi Pulut Malat, Kakua, IR72, Khakibinni. But in the susceptible cv. IR58, chitinase activity was detected only 36 h after inoculation. Western blot analysis showed that class 1 and class 2 chitinases were induced following Rhizoctonia solani infection of these cultivars. The % RLH and the number of infection cushions were negatively correlated with the level of chitinase activity. Moderately resistant rice cultivars had higher levels of chitinase activity and lower disease severity and numbers of infection cushions formed compared to IR58.