The influence, upon male rat s mating behavior, of Korean Panax Ginseng administered for 3 and 5 days was investigated by direct behavioral observation and also by counting the number of copulation plugs the animals deposited. Four쇼-four male albino rats were used. Part of the animals received ginseng for 3 days (ginseng-3 day group, N= 12) or for 5 days(ginseng-5 day group, H=10), while the remaining animals received saline for 3 days (saline-3 day group, N=12) or for 5 days (saline-S day group, N=10). Each animal belonging to the 2 ginseng groups received subcutaneously 0.5 ml/100 g body weight of ginseng alcohol extract solution (4 mg of the ethyl alcohol extract in 1 ml of physiological saline), and each rat belonging to the 2 saline groups received the same amount of saline per day. During the dark period of the light-dark cycle on the next day following the last drug administration, a female rat in the artificial estrus was introduced to each male and the mating behavior was observed for 45 minutes. The observation session was divided into two parts and, in the early part which terminated with the first ejaculation and succeeding intromission, following behavioral measures were taken: mounting latency, intromission latency, inter-intromission period, ejaculatory latency(time from the first intromission until the first ejaculation), occurrence of mounting with intromission, occurrence of mounting without intromission, and postejaculatory interval. Behavioral measures taken in the later part of the session after the first ejaculation were: occurrence of mounting with intromission, occurrence of mounting without intromission, and occurrence of ejaculation. Immediately after the behavioral observation session the experiment turned to measure, for 10 days, the number of copulation plug which each pair of rats deposited. Following results were obtained: 1. After several mountings mounting with intromission, males of the 2 ginseng groups finished the first ejaculation significantly earlier than the corresponding 2 saline groups did. 2. The postejaculatory latency was significantly reduced in the ginseng-5 day group compare with the value of the saline-5 day group and also compared with the value of the ginseng-3 day group. 3. The 2 ginseng groups ejaculated significantly more often in 45 minutes observation session than the corresponding 2 saline groups did. 4. The number of copulation plug deposited in 10 days by the animals of the 2 ginseng groups. significantly exceeded the number deposited by the corresponding 2 saline group animals. The animals of the ginseng-5 day group deposited copulation plugs significantly more than the animals of the ginseng-3 day group did. It is inferred from the above results that the ginseng facilitates mating behavior of male rats, and that the degree of facilitation may be influenced by the duration of drug administration.