Royal Made Ping An Dan (PAD) is a royal clandestine prescription of the Qing Dynasty Imperial hospital for emperors, empresses, ministers, imperial maids and eunuchs. Experimental study confirmed; (1) PAD had apparent peripheral effect in inhibiting vomiting and improving mental state (P < 0.05). (2) PAD possessed markedly sedative effect (P < 0.05). (3) PAD was able to strengthen the defence ability of gastric mucosa and decreased its damage induced by chemical irritation. (4) PAD could markedly relieve the spasm of intestinal smooth muscle in vitro. (5) PAD could inhibit the growth of common pathogenic bacteria in intestine and stomach such as B. coli and B. dysenteriae. (6) The study of toxicology suggested that PAD was safe for clinical use. The clinical results showed that PAD possessed the effect in preventing 274 persons on motion sickness. The total effective rate of PAD group was 83.9%, while that of Dramamine group was 60.8%. PAD revealed better effect than that of Dramamine. Therefore, the authors realize that PAD is a better preventive drug for motion sickness.