OBJECTIVE To investigate the effect of early exposure to allergen (ovalbumin, OVA) on rat asthmatic models. METHODS Neonate rats were randomly divided into negative control group, asthmatic model group, low dose group and high dose group, with 8 in each. The rats of low dose group and high dose group were injected subcutaneously with 2 g/L OVA 0.1 mL and 10 g/L OVA 0.1 mL separately on the 1st day. OVA was given in asthmatic model group, low dose group and high dose group for allergization 6 weeks later and then asthmatic models were made. The pathologic changes of lung tissue, cell count and differentiation of bronchoalveolar lavage fluid (BALF) and serum interleukin-4 (IL-4), interferon-gamma (IFN-gamma), OVA-specific IgE and OVA-specific IgG were observed. RESULTS The airway inflammation in both low dose group and high dose group was less severe than that in asthmatic model group. Total cell count of BALF and the ratio of eosinophil and neutrophil of both groups were decreased significantly compared with asthmatic model group. IL-4 and OVA-specific IgE were markedly decreased, while IFN-gamma was significantly increased in both low dose group and high dose group compared with asthmatic model group respectively. There was no significant difference in IL-4, IFN-gamma and OVA-specific IgE between high dose group and control group. The serum OVA-specific IgG was elevated significantly in asthmatic model group, low dose group and high dose group compared with control group, and it was higher in high dose group than in asthmatic model group. CONCLUSIONS Early exposure to OVA after birth could inhibit the airway inflammation and OVA-specific IgE increasing induced by OVA in grown-up rats, and the mechanisms might be related to formation of immunology tolerance.