The activity-guided fractionation of the extract of the herb of Prunella vulgaris (Labiatae) led to the isolation of four triterpenes, i.e., betulinic acid, ursolic acid, 2α,3α-dihydroxyurs-12-en-28-oic acid, and 2α-hydroxyursolic acid. One of these compounds, 2α,3α-dihydroxyursolic acid, demonstrated significant inhibition on the release of β-hexosaminidase from the cultured RBL-2H3 cells in a dose-dependent manner; the IC50 value was calculated to be 57 μM. When the isolated compounds were tested for their effects on the production of nitric oxide from cultured murine macrophages, RAW 264.7 cells, ursolic acid and 2α-hydroxyursolic acid exhibited strong inhibitory activities (IC50 values, 17 and 27μM, respectively).