Musoca from bovine small intestine was homogenized in Krebs-Ringer phosphate buffer, pH 7.8 the homogenate centrifuged at 16300 X g, and the supernatant solution filtered through cheesecloth to remove lipid material. The filtrate was centrifuged at 105000 X g and the supernatant solution chromatographed on DEAE-cellulose. The major peak of DNase II activity, eluted with 20 mM phosphate - 10 mM EDTA buffer, pH 7.8, was purified further by ion-exchange chromatography on CM-cellulose and gel filtration on Sephadex G-100. The enzyme was purified 78-fold in 13% yield. Evidence was adduced to indicate that the second minor peak of DNase II activity, eluted from the DEAE-cellulose by a potassium chloride gradient in the 20 mM phosphate - 10 mM EDTA buffer, was an artifact arising from the presence of significant amounts of DNA in the 105000 X g supernatant. The enzyme degraded DNA endonucleolytically to 3'-PO4, 5'-OH oligonucleotides and is similar in its properties to DNase II from other tissues.