A methanol extract of hops of Humulus lupulus (L.) showed inhibitory activity against rat liver diacylglycerol acyltransferase (DGAT). From DGAT inhibitory activity-guided fractionation, two chalcones were isolated. One was identified as xanthohumol and the other was found to be a new product designated xanthohumol B. The structure of xanthohumol B was shown to be 6-[3,4-dihydro-3,5-dihydroxy-7-methoxy-2,2-dimethyl-2H-benzo[b]pyrano ]- 3-(4-hydroxyphynyl)-2-propen-l-one by spectroscopic studies including various NMR measurements. Xanthohumol and xanthohumol B inhibited DGAT activity with IC50 values of 50.3 and 194 microM in rat liver microsomes, respectively. They showed preferential inhibition of triacylglycerol formation in intact Raji cells, indicating that they inhibit DGAT activity preferentially in living cells.