A complete amino acid sequence of extracellular Bacillus circulans RNase was established and compared with a structure of B. amyloliquefaciens RNase. Gln15, Gly65 and Gln104 in B. amyloliquefaciens RNase were found to be replaced by Leu, Ala and Lys, respectively, in B circulans RNase. Catalytic properties of B. circulans RNase were studied.