Abstract: The effects of different harvesting time under the same habitat on the chemical constituents of essential oil obtained by steam distillation from fructus viticis, which were the dried fruits of Vitex trifolia Linne var. simplicifolia Cham.(synonym:V.rotundifolia Linne fil.), were studied. The essential oil contents were 0.35%, 0.41%, and 0.39% during different harvesting time, namely Aug., Sep. and Oct. respectively. According to the order of the harvesting time, 19, 22 and 29 compounds in the different essential oils were detected by GC-MS, respectively, but only 5 compounds in three different essential oils are in common. The main compounds in all essential oils were terpenoids, whose contents were 99.6%, 90.2% and 94.1%, respectively. This result implies that most of the chemical constituents among three different essential oils were different. On the other hand, the types of three main terpenoids were pinanes, acetoxy-p-menthanes, and p-menthane-diene during the three different harvesting times, respectively. These chemical types have similar structures that will be used for further investigating their interrelation in fructus viticis in order to optimize its quality.