Twelve polycyclic diterpenes have been isolated from the roots of Euphorbia kansui. Nine were assigned with an ingenol skeleton, 20-O-(2'E,4'E-decadienoyl)ingenol (1), 20-O-(2'E,4'Z-decadienoyl)ingenol (2), 3-O-(2'E,4'Z-decadienoyl)ingenol (3), 3-O-(2'E,4'E-decadienoyl)ingenol (4), 3-O-(2'E,4'Z-decadienoyl)-5-O-acetylingenol (5), 3-O-(2'E,4'Z-decadienoyl)-20-O-acetylingenol (6), 3-O-(2'E,4'E-decadienoyl)-20-O-acetylingenol (7), 20-O-(decanoyl)ingenol (8), and 5-O-(2'E,4'E-decadienoyl)ingenol (9), and three with a jatrophane skeleton, kansuinins A (12), B (11), and C (10). Compounds 1, 2, 5, 9, and 12 are new compounds, while 4 and 7 were assigned with new geometric configurations. Their structures were elucidated by spectroscopic and chemical analysis. In vitro treatment of cultured individual Xenopus cells at the blastular stage with 1-9 arrested cleavage significantly (0.5 microg/mL of each compound resulted in >75% cleavage arrest). Of the three jatrophane diterpenes (10-12), only kansuinin B (11) showed any activity, resulting in 87% cleavage arrest at 50 microg/mL.