Vitamin C is traditionally regarded to be beneficial for asthma, however the benefit is still controversial. In the present study, high dose vitamin C was supplemented to ovalbumin (OVA)-sensitized and challenged mice to evaluate the effects of dietary vitamin C on allergic asthma. In this study, the experimental mice were divided into four groups, including nonsensitized control, dietary control, positive control (cured ip with dexamethasone), and high dose vitamin C supplementation (130 mg of vitamin C/kg bw/day by gavage for 5 weeks). Differential leukocyte counts, levels of inflammatory mediators, as well as type 1 T-helper lymphocytes (Th1)-type and type 2 T-helper lymphocytes (Th2)-type cytokines in the bronchoalveolar lavage fluid (BALF) were determined. The results showed that both high dose vitamin C supplementation and dexamethasone treatments significantly (P < 0.05) decreased eosinophilic infiltration into BALF. High dose vitamin C supplementation significantly increased the secretion ratio of interferon (IFN)-gamma/interleukin (IL)-5 cytokines. This study suggests that high dose vitamin C supplementation might attenuate allergic inflammation in vivo via modulating the Th1/Th2 balance toward the Th1 pole during the Th2-skewed allergic airway inflammation and decreasing eosinophilic infiltration into BALF.