Streptococcal nuclease was completely purified by stepwise CM-Sepharose column chromatography from crude extracts isolated from Streptococcus sp. The active enzyme fraction was eluted with the buffer containing 0.2 M NaCl. The purified enzyme showed a homogeneity on SDS PAGE and had a molecular weight of 35,000 daltons. The optimum pH and temperature for the enzyme were 9.0 and 50℃, respectively.