Animal experiments were performed to develop Salvia plebeia (Labiatae) as a medicinal herb with sedative and gastroprotective activities; the former activity was measured using a pentobarbital-induced assay and the latter activity was measured in two gastric lesion-induced assays (HCl/EtOH-induced and indomethacin/bethanechol-induced assays) in mice. The MeOH extract and its EtOAc fraction were effective, although the former was less active than the latter. Rosmarinic acid (RA) isolated from S. plebeia was active in the same method at 10 and 20 mg/kg (p.o.). HPLC quantification demonstrated that RA comprised the largest proportion (28.5% of the MeOH extract, 33.0% of EtOAc extract; 4.46% of dry weight) of S. plebeia. The contents of five other compounds were much less than that of RA, although the contents of the three glycosides, 6-hydroxyluteolin 7-O-glucoside (0.28% of dry weight), cynaroside (0.35%) and nepitrin (0.43%) were higher than those of the two aglycones, quercetin (0.024%) and eupatilin (0.058%). The HPLC method was validated in terms of linearity, precision, accuracy and reproducibility. These results suggest that the main polyphenol, RA, plays a major role in the sedative and gastroprotective effects of S. plebeia.