Objectives : The root bark of Morus alba L. (Mori Cortex Radidus; MCR) has been traditionally used to reduce heat from the lungs, soothe asthma, and edema and to promote urination. In this study, we investigated the effect of MCR ethanol extract on ovalbumin (OVA)-induced allergic asthma in mice. Methods : Mice were sensitized at day 0, 7 and 14 with 0.2% OVA and then airway challenged at day 21, 23, 25, 27 and 29 to induce allergic asthma. MCR extracts at doses of 50 and 100 mg/kg body weight (bw) were orally administered during OVA challenge once per a day. The levels of allergic mediators such as histamine, OVA-specific IgE, IFN-${gamma}$ and IL-4 were measured in the sera of mice by ELISA. The histopathological change of lung tissues was observed with hematoxylin and eosin (H&E) staining. Results : MCR extract significantly decreased not only the serum levels of histamine, OVA-specific IgE, and IL-4 compared with those of OVA control group, but significantly increased the serum level of IFN-${gamma}$. In H&E staining, MCR extract inhibited the infiltration of inflammatory cells and bronchiolar damage with epithelial thickening in lung tissues of OVA-induced asthma mice. Conclusions : These results indicate that MCR extract inhibits lung damage by asthma through regulating the allergic immune response, suggesting that MCR may be used as a useful agent for the treatment of allergic asthma.