It has been known that the ginseng extracts activate the lipid metabolism in animal body. The experiments were undertaken to elucidate the effects of total, diol, and trial saponin of ginseng on the activities of acyl Co-A synthetase and hydroxyacyl Co-A dehydrogenase involved in fatty acid metabolism in normal albino rat liver. The acyl Co-A synthetase activity, in vitro, was increased by 20% with treatment of 2.5${ imes}$10-3% total saponin, by 14% with 2.5${ imes}$10-3% diol saponin, arid 30% with 2.5${ imes}$10-4% triol saponin, respectively. And the enzyme activity was increased by 27% at 2 hours after intraperitoneal injection of total saponin. Hydroxyacyl Co-A dehydrogenase activity, in vitro, was increased by 77% with 10-4% total saponin, by 64% with 10-2% diol saponin, and by 72% with 10-3% triol saponin, respectively. Also, the enzyme activity, in vivo, was increased by 15.3% and 33% at 2 hours and 4 hours.