Structural modification is still a popular and important route in the forest chemical field for finding novel tricyclic diterpenes with more potential bioactivities and broad bioactive spectra. In this study, a series of dehydroabietylamine derivatives containing tricyclic diterpene structures were synthesised through oxidation in the 7th position of ring B and nitrification in the 12th position of ring C using dehydroabietylamine as the starting material. Structures of the synthesised compounds were confirmed by IR, (1)H-NMR, (13)C-NMR, MS and HRMS. The cytotoxicities of these compounds against PC-3 (human prostate carcinoma cell line) and Hey-1B (human ovarian carcinoma cell line) cells by the MTT assay were investigated. The results showed that the presence of a nitro group at 12th position and a carbonyl group at 7th position resulted in an increase of cytotoxic activity. Our findings present more evidence, showing the relationship between the chemical structure and biological function.