Introduction: Nasal cavities are responsible for filtrating inhaled air, so they may be damaged by air pollution. Aim: To evaluate protein synthesis on epithelial cells and submucosal glands, and the epithelial height in nasal cavities of rats exposed for 6 months to air pollution. Material and Methods: 16 female Wistar rats (2.5 months old) were used. 8 rats were housed, during 6 months, in Cubatão (petrochemical area), and a control group in Ubatuba where air pollution is considered null. During the study the highest pollutant level didn't reach attention levels. Its effects were evaluated by a silver staining technique called AgNOR, that measures protein synthesis. AgNOR area was measured at epithelial cells and submucosal glands of nasal mucosa. We also measured epithelial height. Results: AgNOR areas were smaller in the epithelial cells of all animals. AgNOR areas in epithelial cells and submucosal glands were smaller in those exposed to air pollution. Epithelial height was also smaller in this group, although we could not establish its correlation with AgNOR area. Conclusion: Rats exposed, for 6 months, to low levels of petrochemical pollution developed nasal mucosa atrophy, characterized by decreasing in protein synthesis.