OBJECTIVE The effects of anti-ulcerogenic drugs are dependent on the increase in prostaglandin production and reduction in leukotriene production in the gastric mucosa. Montelukast is an anti-asthmatic drug, a selective reversible cysteinyl leukotriene D4 receptor antagonist. In this study, we aimed to evaluate the anti-ulcerogenic effect of montelukast and to investigate the relationship between its anti-ulcerogenic effect and polymorphonuclear leukocyte infiltration in the gastric tissues. METHODS Male Sprague-Dawley rats were separated into five groups. Distilled water (control group), famotidine (40 mg/kg), and montelukast (5, 10 and 20 mg/kg) were given orally (gavage). Thirty minutes later, indomethacin (25 mg/kg) was administered to all the groups. Six hours later, the animals were sacrificed by decapitation. The ulcer indexes for each stomach and the ulcer inhibition rates for each group were calculated, and the stomachs were later evaluated histopathologically (polymorphonuclear leukocyte infiltration). RESULTS Ulcer inhibition rates were as follows: famotidine 96.14% and montelukast 59.96%, 72.65% and 76.97% (5, 10 and 20 mg/kg, respectively). Montelukast (10 and 20 mg/kg) showed effects similar to those of famotidine histopathologically. CONCLUSIONS In this study, it was observed that there was a relationship between the anti-ulcerogenic effect of montelukast and polymorphonuclear leukocyte infiltration in the gastric mucosa, and montelukast behaved as an anti-ulcerogenic drug both macroscopically and microscopically.