Chemical examination of the marine sponge Rhabdastrella aff. distincta resulted in the isolation of six new isomalabaricane triterpenes, rhabdastrellins A−F (1−6), which were present as minor components, along with stellettins L and M. Their structures were elucidated on the basis of extensive spectroscopic data analyses and comparison with spectroscopic data of known analogues. The cytotoxicity of compounds 1−6 against a small panel of human tumor cell lines was also evaluated.