Sodium fluoride is one of the most spread environmental substances because of its presence in soil, water and air. The present work demonstrated that sodium fluoride produced variable histological alterations in the lungs of rats. These changes appeared as severe congestion of the blood vessels with blood extravasation, increased number of macrophages with cellular infiltration, thickened septa with decreased alveolar spaces .Ruptured septa with enlarged air spaces were also noticed. Presence of haemosiderin granules was remarkable.The electron microscopic study revealed collapsed bronchioles with distorted cilia. Mitochondria of mucosal cells were swollen with disrupted cristae, and their nuclei were either heterochromatic or pyknotic. The alveoli showed pneumocyte type II with lamellar bodies, heterochromatic nucleus with irregular nuclear membrane. The mitochondria were either normal or swollen with loss of cristae.These changes might be due to oxidative stress and generation of reactive oxygen radicals. The recovery period found to reduce the observed harmful effect of sodium fluoride on the lungs.