1. Proteinases a and c from the venom of A. halys blomhoffii have been purified by successive use of ion-exchange chromatography and gel filtration. From 32.7 g of the lyophilized venom 138 mg of purified proteinase a and 2.69 g of purified proteinase c were obtained. The purified preparations of proteinases a and c are essentially homogeneous as observed by sedimentation in the ultracentrifuge, free-boundary ele-ctrophoresis and column chromatography. 2. The values of the sedimentation constants extrapolated to zero concentration, s20˚, w, are 3.63 S and 4.94 S for proteinase a and c, respectively. The diffusion constant for proteinase c, D˚20o w, is 5.88 × 10−7cm2 sec−1. The partial specific volume of proteinase c, D˚20, w, is 0.695 ml/g and its intrinsic viscosity, [n], is 0.046 dl/g. The molecular weights of proteinases a and c are computed to be about 50,000 for the former and about 70,000 for the latter. Free-boundary electrophoreses give isoelectric points of pH 6.0 for proteinase a and 3.85 for proteinase c. Their absorbancies A1%1cm at 280 mμ, are 9.08 and 10.98 for proteinases a and c, respectively. Their contents of nitrogen are 13.83 and 13.90 per cent and those of polypeptides 76.5 and 91.2 per cent for proteinases a and c, respectively. 3. Both proteinases a and c contain sugars in their molecules, 13.6 per cent for the former and 8.46 per cent for the latter.