Three new arylnaphthalene lignans, namely phyllanthusmins A-C, together with nine known compounds were isolated and characterized from the stems and roots of Phyllanthus oligospermus by a bioassay-guided purification. The structures of the new compounds were elucidated by means of spectroscopic data interpretation. Among them, phyllanthusminA displayed significant cytotoxicity against KB and P-388 cancer cell lines.