The present study was carried out to detect histopathologic lesions in different rat organs after chronic exposure to formaldehyde vapor. Forty adult albino Wistar rats were used in this experiment. Animals were divided into two groups; Control group (n=10; 5 males and 5 females) which were not exposed to formaldehyde at all, while the remainders regarded as the experimental group (exposed to formaldehyde for 21 days, n=30; 15 males and 15 females). The histopathologic examination in our study revealed several changes in exposed group such as; chronic tracheitis, squamous metaplasia of lining epithelium and tracheal glands with occurrence dysplasia in the lining epithelium, interstitial pneumonia, hydropic degeneration in the hepatocytes, epidermal hyperplasia, interstitial glomerulonephritis with atrophy of glomeruli. We concluded that the overexposure of formaldehyde produced lesions in different organs but their toxic effects were seen predominantly in respiratory system.