Five undescribed monoterpene-chalcone conjugates (1-5), one undescribed hypothetical precursor of diarylheptanoid (6), two undescribed diarylheptanoids (7–8), and fourteen known compounds (9–22) were isolated from the seeds of Alpinia katsumadai. Their structures were elucidated through the interpretation of HRESIMS, NMR, ECD, and X-ray diffraction data. MTT assays on human cancer cell lines (HepG2, A549, SGC7901, and SW480) revealed that compounds 3–8, 11, and 13 exhibited broad-spectrum antiproliferative activities with IC50 values ranging from 3.59 to 21.78 μM. B cell lymphoma 2 was predicted as the target of sumadain C (11) by network pharmacology and verified by homogeneous time-resolved fluorescence assay and molecular docking.