Two new gamma-lactones, saccopetrin A (1) and saccopetrin B (2), together with 10 known compounds have been isolated from the roots of Saccopetalum prolificum. Their structures were established by spectroscopic and chemical methods. The absolute configuration of 1 was determined by chemical transformation and the Mosher method. Cytotoxic activities were evaluated against several different cell lines. Compound 2 exhibited stronger cytotoxic activities than 1 against KB and HCT-8 cell lines at a concentration of 10(-5) mol/L.