The effect of ovalbumin (Ova) sensitization on pulmonary C-fiber sensitivity was investigated. Brown-Norway rats were sensitized by intraperitoneal injection of Ova followed by aerosolized Ova 3 times/week for three weeks. Control rats received the vehicle. At the end of the third week, single-unit fiber activities (FA) of pulmonary C-fibers were recorded in anesthetized, artificially ventilated rats. Our results showed: 1) Ova-sensitization induced airway inflammation (infiltration of eosinophils and neutrophils) and airway hyperresponsiveness in rats. 2) Baseline FA in sensitized rats was significantly higher than that in control ones. 3) Similarly, the pulmonary C-fiber response to right-atrial injection of capsaicin was markedly higher in sensitized rats, which were significantly amplified after the acute Ova inhalation challenge. 4) Similar patterns, but smaller magnitudes of the differences in C-fiber responses to adenosine and lung inflation were also found between sensitized and control rats. In conclusion, Ova sensitization elevated the baseline FA and excitability of pulmonary C-fibers, and the hypersensitivity was further potentiated after the acute Ova inhalation challenge in sensitized rats. Chronic allergic inflammatory reactions in the airway probably contributed to the sensitizing effect on these lung afferents.