Ethanol extract of the seeds of Licaria puchury-major, a Brazilian herbal medicine, was found to inhibit cell proliferation in human leukemia cell line (Jurkat) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Bioassay-guided fractionation of the active components led to the isolation of one phenylpropanoid (1) and ten neolignans (2—11). The apoptosis-inducing activity of the compounds showing cytotoxicity in Jurkat cells was assessed by flow cytometric analysis. Among the identified neolignans, compounds 3, 4, 6 and 7 which have similar molecular structures, showed apoptotic activity. To elucidate the mechanism of apoptosis induction by neolignans, intracellular caspase-3, -8 and -9 activity in Jurkat cells was evaluated. Compound 4 markedly elevated the activity of caspase-3 and -9.