Marine sponges are known to be a source of diverse sterols. In our study on the cytotoxic components of the marine sponge Spirastrella abata, $5{alpha},8{alpha}-epidioxy;{Delta}^6$ sterols (1-5) and $5{alpha},8{alpha}-epidioxy;{Delta}^{6,9(11)}$ sterols (6-7) were isolated. The structures were identified based on the analyses of $^1H-NMR,;^{13)C-NMR$, and MS data. These compounds were assayed for cytotoxicity against 5 human solid tumor cell lines including A549, SK-OV- 3, SK-MEL-2, XF498, and HCT15.