From an ethyl acetate extract of twigs and barks of Dacrydium elatum a new diterpenoid named dacrydianone (1), together with lambertic acid (2), three ecdysteroids: 20-hydroxyecdysone (3), ajugasterone C (4), ponasterone A (5), and daucosterol (6), has been isolated. Their structures were elucidated by an extensive analysis of the UV/Vis, FT-IR, MS and NMR spectra as well as comparison with those in published literature. The EtOAc extract and the isolated compounds 1–5 were evaluated for their cytotoxicity on four cancer cell lines: breast cancer (MCF-7), lung cancer (Lu-1), liver cancer (HepG2) and human oral cancer (KB). The EtOAc extract and compound 2 showed a medium activity on four tested cancer cell lines, while compounds 3 and 5 exhibited week activity on these cell lines. Compounds 1 and 4 did not show activity on the tested cell lines.