Two diterpene lactones, sarcophinone(1) and iso sarcophinone(2), which are biogenetically related to the sarcophine, were isolated from the soft coral Sarcophyton molle Tix. Dur. iso Sarcophinone 2 is a new compound. Its structure was determined to be C 1 epimer of sarcophinone by spectroscopic methods. Bioassay showed that both sarcophinone(1) and iso sarcophinone(2) had potent cytotoxicity toward Ehrlich and S180 tumor cell lines.