A series of new C11 cyclopentenones 1-7 was isolated, together with four known metabolites 9/10, 12 and 13, from the extract of the didemnid ascidian Lissoclinum RCA sp.The other didemnid ascidian Diplosoma sp.contained didemnenones 1, 2 and 5, and five known metabolites 8-12.The structures of 1-7 were elucidated by spectroscopic Side Tables analyses.Cytotoxicity of the isolated compounds was evaluated against three human cancer cell lines (HCT116, A431 and A549).