The antimitotic effect of cornin extracted from bovine liver was studied. Obtained results are summerized as follows. 1) Bovine liver cornin has antimitotic effect on sea urchin eggs. But the author has not recognized the morphological differencies on their, development when observing sea urchin eggs under the electron microscopy. 2) The mitotic rate of Ehrlich ascites carcinoma cells decreased by injections of bovine liver cornin and also the DNA synthesis was inhibited in propotion to the doses of bovine liver cornin. 3) The mitotic rate in regenerating rat liver decreased by injections of bovine liver cornin. 4) The inhibition of bovine cornin on the DNA synthesis in regenerating rat liver, was the most strongest when administered in equal to the physiological concentration. 5) Above results suggest the existense of the higher mitotic autoregulating center.