Antiarisin A and B (1 and 2), together with seventeen known compounds (3-19), were isolated from the EtOAc extract of the stem of Antiaris toxicaria Lesch. Their structures were determined on the basis of spectroscopic analyses and chemical methods. Most of the compounds were reported for the first time from the Antiaris genus and firstly studied for their proliferative and differentiative activity on osteoblast-like cells. Screening results indicated that, at the concentration of 10(-8) M, benzofuran lignans 5, 6, 11 and 13 could significantly stimulate the proliferation of UMR106 cells, while 8, 9, 11, 14, 15 and 17 could enhance ALP (alkaline phosphatase) activity.