The antimitotic effect of cornin extracted from dog intestine, are summarized as follows. 1. Canine intestine cornin (CIC) inhibit the proliferation of HeLa cell in tissue culture. It's antimitotic effect, however, increases depend on the cornin dose per cell. 2. CIC is stable substance. Antimitotic effect of CIC does not decrease after stocking in desiccater over 3 years, and also 2 days preincubation in 37℃. DTT treated CIC show no differences with untreated CIC in growing HeLa cell. 3. Both dialysable and nondialysable fractions show antimitotic effect to HeLa cell. And nondialysable fraction is more effective. 4. Ultrafiltration is done by Diafilter membrane. The most effective fraction of molecular weight is over than 55,000. The next is molecular weight 20,000~55,000, the third is molecular weight below 10,000. The component molecular weight 10,000~20,000 is slightly effective. 5. The antimitotic effect of molecular weight over than 55,000 fraction decreases by 2 days treatment in 0.025% trypsin at 37℃. 6. CIC is separated in 3 fractions by Sephadex G200 column. The most effective fraction is FⅢ. It suggests that the antimitotic action of CIC is more effective in relatively small molecular weight of molecular weight over than 55,000 fraction.