During alcoholic fermentation trans- and cis-resveratrol were rapidly extracted from grape skin along with the rise in the alcoholic concentration and reached equilibri-um six days after the start of maceration. The increase of trans-resveratrol was shown to be ahead of that of the cis isomer, but the trans isomer decreased at the late stage. It was, therefore, assumed that trans-resveratrol would be converted to the cis isomer by the action of a possible yeast isomerase. In addition,on the process of malolactic fermentation resveratrol levels were found to increase accompanied by a decrease in piceid concentration. This means that the increase resulted from the hydrolysis of piceid by v-glucosidase activity produced by lactic acid bacteria involved in the malolactic fermentation. (Received Sep. 30,2003 ; Accepted Feb. 24,2004)