The cultural and biological characteristics of Rhizoctonia solani and R.cerealis isolates obtained from rice(Oryza sativa), maize(Zea mays) and wheat(Triticum aestivum) under different cultural media,temperatures,carbon sources,nitrogen sources, pH values and illumination conditions were compared in this study. The results showed that the tested Rhizoctonia isolates from three crops varied significantly in colony growth rate, colony and sclerotium colour,sclerotial amount and sclerotium distribution in the Petri dish. Czapek and PSA media were found to be the most suitable media for mycelial growth of R.solani from rice and maize and R.cerealis from wheat. For R.solani isolates from rice and maize, the temperatures for mycelial growth were in the range of 10-35 ℃ with optimum at 25-30 ℃,whereas R.cerealis isolates from wheat were able to grow at 5-30 ℃ with optimum at 20-25 ℃. In the tested carbon sources,all tested isolates were able to utilize soluble starch, sucrose and glucose. However,the R.solani isolates from rice and maize were the poorest in utilizing mannitol, and the R.cerealis isolates from wheat were the poorest in utilizing lactose. All tested Rhizoctonia isolates were found to grow better on five tested nitrogen sources,i.e. potassium nitrate,sodium nitrite,ammonia sulfate,urea and L-leucine,but the sclerotial formation of all tested Rhizoctonia isolates on these five nitrogen sources varied significantly. For the mycelial growth and sclerotial formation of Rhizoctonia isolates from three crops,the pH ranges were 4-10 with optimum at pH 6. The results also indicated that the mycelial growth of all tested isolates under different illumination conditions were not significantly different,but the illumination conditions could affect the sclerotial amount and the colour.