Phytochemical analysis of the underground parts of Polianthes tuberosa has resulted in the isolation of four new spirostanol saponins with five monosaccharides (1-4). Their structures were determined by spectroscopic analysis, including extensive 1D and 2D NMR data, and the results of hydrolytic cleavage. The cytotoxic activities of 1-4 against HL-60 human promyelocytic leukemia cells and HSC-2 human oral squamous cell carcinoma cells are reported.