The aim of this study is to evaluate if mitomycin C (MMC), applied topically at the site of maxillary antrostomy in experimentally inflamed maxillary sinuses, may reduce postoperative ostial stenosis without any harmful effect. Twenty-four rabbits with experimentally induced maxillary sinusitis underwent maxillary antrostomy bilaterally. MMC at a concentration of 0.4 or 1 mg/ml was applied at the site of antrostomy on the right whilst the antrostomy site on the left served as the control. Half of each MMC concentration group of animals were killed after 3 weeks, and the remaining half after 6 weeks. For every rabbit, the areas of antrostomies were measured and mucosal specimens around the ostia were obtained for microscopic evaluation at the time of antrostomy and killing. Within each MMC concentration group, MMC-treated antrostomies were significantly wider than those of the controls (P < 0.05), even after 6 weeks. However, comparison of the areas of MMC-treated antrostomies between the two MMC concentration groups did not show any significant difference (P > 0.05). No systemic side effect or permanent mucosal damage was detected. These results suggest that postoperative topical MMC at a concentration of 0.4 mg/ml can be used to prolong the patency of maxillary antrostomy in an inflammed sinus.