Objectives : The root of Peucedanum japonicum Thunberg (Peucedani Japonici Radix; PJR) has been traditionally used as an herbal medicine for the treatment of anti-headache, anti-paralysis, anti-cancer, vascular protection, and blood pressure regulation. In this study, we investigated the anti-allergic effect of PJR water extract on ovalbumin (OVA)-induced allergic asthma in mice. Methods : Mice were sensitized at days 1, 8 and 15 with OVA and airway challenged at days 22, 24, 26, 28, and 30 to induced allergic asthma. PJR-W extract at doses of 100 and 300 mg/kg/body weight (bw) was orally administered during OVA challenge once per a day. The levels of allergic mediators such as immunoglobulin (Ig) E, and Th1/Th2 cytokines (IFN-${gamma}$ and IL-4) were measured in the sera of mice by ELISA. The histological change of lung tissue was observed with hematoxylin and eosin (H&E) staining. Results : The administration of PJR-W extract significantly decreased the serum levels of IgE, IL-4, and IFN-${gamma}$ compared with those of OVA control group. In H&E staining, PJR-E extract inhibited OVA-induced airway inflammation and the inflammatory cells infiltration in the peribronchial regions of the lung. Conclusions : These results indicate that PJR-W extract has an anti-inflammatory and anti-allergic effect on allergic response through the down-regulation of allergic mediators, suggesting that this herb may be used as a useful source for the treatment of allergic inflammatory diseases such as asthma.