Many investigations have demonstrated the prophylactic effect of Nigella sativa on asthma disease. One of its active constituents is α-hederin. In the present study, the preventive effect of two different concentrations of α-hederin on tracheal responsiveness and lung inflammation in ovalbumin-sensitized guinea pigs was examined. Forty male adult Dunkin-Hartley guinea pigs were randomly divided into the control (C), sensitized (S) and sensitized pretreated groups with thymoquinone (3 mg/kg i.p., S + TQ), low-dose α-hederin (0.3 mg/kg i.p., S + LAH) and high-dose α-hederin (3 mg/kg i.p., S + HAH). The responsiveness of tracheal smooth muscle (TR) to methacholine, histamine and ovalbumin was assessed. Moreover, total and differential white blood cell counts in lung lavage fluid were examined. Compared with the S group, the mean EC50 value in the S + LAH group increased significantly (p < 0.05). The mean EC50 value of histamine contraction in the S + LAH and S + HAH groups was significantly higher than in the S group (p < 0.05). In all pretreated groups, the TR to ovalbumin decreased in comparison to the S group (p < 0.001). Both the S + HAH and S + LAH groups showed significantly decreased TR compared to the S + TQ group (p < 0.01-p < 0.01). Total WBC and eosinophil counts in all pretreated groups decreased significantly in comparison with the S group (0.001-0.01). There was a significant increase in neutrophil, lymphocyte and monocyte counts in the pretreated groups compared to the S group (p < 0.001-p < 0.05). The basophil count in the S + TQ and S + HAH groups was significantly lower than in the S group (p < 0.01-p < 0.05). This study suggested that α-hederin has anti-inflammatory and bronchodilatory effects like thymoquinone.