Five new 7α-hydroxyeunicellin-based diterpenoids, designated as cladieunicellins M-Q (1-5), were isolated from a Formosan octocoral Cladiella sp. The structures of 1-5 were elucidated on the basis of spectroscopic methods and by comparison of the data with those of the related metabolites. Cytotoxicity of metabolites 1-5 against the human leukemia Molt 4 and HL 60 is also described. Among them, compounds 1, 3 and 5 exhibited moderate cytotoxicity toward Molt 4 cells with IC₅₀ values 16.43, 14.17 and 15.55 μM, respectively. Preliminary SAR (structure activity relationship) information was obtained from these compounds and their analogues.