Marine invertebrates have been found to be a rich source of bioactive secondary metabolites. In order to search for bioactive compounds, we have studied the chemical constituents from the organic extracts of two Formosan soft corals, Sinularia Scabra and Lemnalia flava. This study had led to the isolation of eight natural compounds, including two new sesquiterpenoids, scabralin A (1) and scabralin B (2) along with two known compounds (3 and 4) from Sinularia scabra, and two new sesquiterpenoids, flavalin A (5) and flavalin B (6) along with three known compounds (4, 7 and 8) from Lemnalia flava. The structures of these compounds were established by the detailed spectral analysis (IR, MS, 1D, 2D NMR) and by comparison of the spectral data with the related known compounds. Lobohedleolide (9), with a great quantity in Lobophytum crassum, have also been modified to compounds 10−19 by chemical conversions with the corresponding reactants via EDC-coupling with an aid of HCl salt of DMAP to yield the related esters and amides.The cytotoxicity of compounds 1, 3−8 and 10¡V19 against the MCF-7 (human breast adenocarcinoma), WiDr (Human colon adenocarcinoma), Daoy (human medulloblastoma), Hep2 (human laryngeal carcinoma), Hep G2 (human liver carcinoma), CCRF-CEM (human T-cell acute lymphoblastic leukemia), and DLD-1 (human colon adenocarcinoma) tumor cell lines were determined. Compound 1 showed moderate activity against the growth of Daoy, Hep2, MCF-7, Hela and CCRF-CEM. Both 15 and 16 exhibited a moderate cytotoxicity against the growth of Hep G2, and compounds 10, 12¡V14, 17 and 18 showed a weak cytotoxicity of it. Compounds 10, 12 and 16¡V18 were found to exhibit moderate inhibition against the growth of CCRF-CEM. Compounds 10, 16 and 18 showed weak activity against the growth of DLD-1. Furthermore, compounds 10, 12 and 14-19 were found to show significant activity against the accumulation of the pro-inflammatory iNOS protein at 10 £gM.