Based on the previous finding of okicamelliaside (OCS), a highly potent anti-degranulation ellagic acid glucoside, in the leaves of Camellia japonica (C. japonica), we evaluated an extract of these leaves and OCS itself for their potential to suppress allergic reactions in vivo. Two conventional animal allergy models were used. In the allergic conjunctivitis model, male S.D. rats were stimulated with anti-ovalbumin (OVA) serum and challenged with OVA/Evans blue mixture. Oral administration of extracts from C. japonica at 1000 mg/kg for 10 days significantly reduced the vascular permeability of conjunctivas. In the second model, male BALB/c mice were stimulated with a Japanese cedar pollen extract and challenged by nasal instillation of the antigen. The sneezing frequency during the 10 min immediately after the challenge tended to decrease by intraperitoneal administration of 0.2 mg/kg of OCS for 24 days. These results suggest that C. japonica extracts (CJE) and OCS prepared from them could be useful to alleviate the symptoms of an immediate-type allergy.