The ultrastructural pulmonary changes which can be induced by Arabian incense, Ma`amoul (mixing incense) exposure was investigated in the present study. Two groups of Wister albino rats were used, one group (n=16) was exposed to 420 g of Ma`amoul for 14 weeks at the rate of 4 g/day in the exposure chamber. The second group of rats was of equal number and used as non-exposed control. At the end of the experimentation period lung tissues were removed from all experimental animals and processed for electron microscopy. Significant ultrastructural changes were noticed in alveolar pneumocytes of exposed animals. These fine changes involved the cell organelles and surfactant material of type II cells. Alveolar septal hypercellularity was due to hyperplasia of the alveolar cells in the affected lung tissue. Neutrophil cell infiltration in the alveolar lumena was accompanied with degenerative and necrotic changes of the alveolar lining cells. Many erythrocytes were extravasated from the distended alveolar capillaries. Alveolar walls revealed deposition of collagen fibrils which contributed in its thickening. It was concluded that exposure to Ma`amoul provokes ultrastructural pulmonary changes which may indicate impaired respiratory efficiency.