Countercurrent chromatographic (CCC) separation and purification of various ribonucleases (RNases) was performed using the small-scale cross-axis coil planet centrifuge (X-axis CPC) with aqueous-aqueous polymer phase systems. RNases B and A were well resolved from each other with an aqueous-aqueous polymer phase system composed of 12.5% (w/w) polyethylene glycol (PEG) 1000 and 12.5% (w/w) dibasic potassium phosphate (pH 9.2) as the mobile lower phase. The commercial RNase A samples obtained from three different companies were also highly purified using the 16.0% (w/w) PEG 1000-6.3% (w/w) dibasic potassium phosphate-6.3% (w/w) monobasic potassium phosphate system (pH 6.6) using the upper phase as the mobile phase. Recombinant RNase Po(1), an RNase T(1) family enzyme, was further successfully separated from the crude extract using the same solvent system with the lower phase used as the mobile phase. The RNase activities were well preserved during the CCC separation. The overall results demonstrate that the small-scale X-axis CPC is useful for a simple and rapid purification of various RNases in a preparative-scale.