An extract of Alnus japonica (Betulaceae) cortex has been traditionally used for purifying blood, and curing feces containing blood, enteritis, diarrhea, alcoholism and cut wounds. Alnus japonica cortex extract significantly inhibited carrageenan-induced paw edema at 1, 2 and 3 hrs after oral administration by 32.8, 24.4, and 46.9%. It also inhibited acetic acid-induced vascular permeability in mice by 15.3 and 28.0% at oral doses of 500 and 1,000 mg/kg, and it significantly reduced the volume of hindpaw of adjuvant-induced arthritis rats at the day 6 and 10 by 22.5 and 18.7% after the sample administration. Alnus japonica cortex extract increased threshold on inflamed paw (Randall-Selitto assay) at 3 hr by 137.5% compared to the control group. It also reduced the number of writhing syndrome dose- dependently.