The total cellular fatty acid compositions of 38 isolates from four Rhizoctonia spp., causal agents of sheath diseases of rice, were characterized by gas-liquid chromatography analysis. The major fatty acids identified were palmitic, stearic, oleic and linoleic acids. Principal component analysis based on the percentage composition of total cellular fatty acids revealed consistently low variability among isolates of a single species and significant differences between the four Rhizoctonia spp. Average linkage cluster analysis also showed that isolates in the same species formed individual clusters on the dendrogram and that each species could be distinguished according to the composition of total cellular fatty acids. These results suggest that the percentage composition of total cellular fatty acids is a distinct characteristic for the causal agents of sheath diseases of rice and that fatty acid analysis will be useful for the differentiation and characterization of these fungi.