Bioassay-guided fractionation and purification of the EtOAc soluble fraction from the MeOH extract of the stem bark of Alnus hirsuta (Betulaceae), using an in vitro HIF-1 assay, led to the isolation of four triterpenoids (1-4) and six diarylheptanoids (5-10). Their structures were determined by comparison with the physicochemical and spectroscopic data in the literature. These compounds were investigated for their effects on the hypoxia-induced HIF-1 activation using an HIF-1a mediated reporter gene assay in AGS cells. Among them, two diarylheptanoids, 2-oxatrycyclo[13.2.2.13,7]eicosa-3,5,7(20),15,17,18-hexaen-10-16-diol (6) and 2-oxatrycyclo [13.2.2.13,7]eicosa-3,5,7-(20),15,17,18-hexaen-10-one (7), inhibited HIF-1 activation dose-dependently with IC50 values of 11.2 microM and 12.3 microM, respectively. These two compounds had no significant cytotoxicity to the AGS cells at the effective concentration for the inhibition of HIF-1 activation.