Galiellalactone analogs (1-4) (including two new compounds), together with their possible precursors (5-9, named pregaliellalactone B-F), were obtained from the solid cultures of an endophytic fungus Sarcosomataceae NO.45-1-8-1. Their chemical structures were elucidated by analyses of HR ESI-TOF MS, 1D-, 2D-NMR, CD spectra and single crystal X-ray diffraction methods. Compounds 5-9, the possible precursors of galiellalactone analogs, were found to exist as enantiomers for the first time. The cytotoxicity of these compounds against six tumor cell lines was examined and preliminary structure-activity relationship (SAR) was also discussed.