Nine new minor diterpenoids, jatrogossones A-I (1-9), and six known analogues (10-15) were separated from an extract of the branches and leaves of Jatropha gosspiifolia. Compounds 4-6 and 10, possessing a 5/11 fused-ring skeleton, and 8, 9, and 13, with a 5/9/5 fused-ring skeleton, represent rare diterpenoid skeletons that have been found only in compounds isolated from plants of the Jatropha genus. The absolute configurations of 1-10 were defined by using a combination of electronic circular dichroism data analysis and single-crystal X-ray diffraction data. The cytotoxicity of the diterpenoids was evaluated using RKO and LOVO colon cancer cells in which regenerating islet-derived protein 3-alpha (Reg3A) is highly expressed. Compound 12 exhibited cytotoxicity against RKO colon cancer cells with an IC50 value of 2.6 μM. Morphological features of apoptosis and antimigration activities were evaluated in 12-treated RKO cells. Compound 12 effectively induced apoptosis of RKO, which was associated with G2/M-phase cell cycle arrest. Flow cytometric analysis showed that the treatment by 12 significantly induced RKO cell apoptosis in a dose-dependent manner.