A phytochemical fractionation of a methanol extract of Ophiopogon japonicus tubers led to the isolation of a new homoisoflavanone, homoisopogon A (1), and three new homoisoflavanes, homoisopogon B-D (2-4). Their chemical structures were elucidated by mass, NMR, and circular dichroism (CD) spectroscopic methods. Homoisopogon A (1) exhibited potent cytotoxicity against human lung adenocarcinoma LU-1, human epidermoid carcinoma KB, and human melanoma SK-Mel-2 cancer cells with IC50 values ranging from 0.51 to 0.66 µM.