Ginsenosides, the main effective components of the root of Panax ginseng, have been reported to modulate morphine action. In the present study, ginsenosides Rd, Rb2, Rgl and Re were divided into two groups according to their effects in mice on morphine-induced hyperactivity and conditioned place preference (CPP). Ginsenosides Rd, Rb2, Rgl had no effect on morphine-induced hyperactivity, but antagonized morphine-induced CPP. On the contrary, ginsenoside Re increased morphine-induced hyperactivity whereas it showed no effect on morphine-induced CPP.Furthermore, Re antagonized the inhibitory effect of the mixture involving Rd, Rb2 and Rgl on the morphine action. These results suggest that ginsenosides with different structures have antagonizing properties in the regulation of morphine-induced reinforcement.