A 20-kDa ribonuclease (RNase) was purified from fresh fruiting bodies of cultured Schizophyllum commune mushrooms. The RNase was not adsorbed on Affi-gel blue gel but adsorbed on DEAE-cellulose and CM-cellulose. It exhibited maximal RNase activity at pH 6.0 and $70^{circ}C$. It demonstrated the highest ribonucleolytic activity toward poly (U) ($379.5{mu}/mg$), the second highest activity toward poly (C) ($244.7{mu}/mg$), less activity toward poly (A) ($167.4{mu}/mg$), and much weaker activity toward poly (G) ($114.5{mu}/mg$). The RNase inhibited HIV-1 reverse transcriptase with an $IC_{50}$ of $65{mu}M$. No effect on [$^3H$-methyl]-thymidine uptake by lymphoma MBL2 cells and leukemia L1210 cells was observed at $100{mu}M$ concentration of the RNase. A comparison of RNases from S. commune and Volvariella volvacea revealed that they demonstrated some similarities in N-terminal amino acid sequence, optimum pH and polyhomoribonucleotide specificity. However, some differences in chromatographic behavior and molecular mass were observed.