Melamine became an adulterant and associated with the pets deaths in some country. The aim of the present study is to evaluate the adverse effects of administration of melamine formaldehyde on the liver, kidney and brain of Wister rats. Rats were randomly designed in to 14 groups (6 rats each) as follows: Groups 1 & 2 were given distilled water (10 ml/kg) for 7 &14 days and served as normal controls, Groups 3-5 were treated orally with melamine formaldehyde (0.88, 1.16, 3.2 mg/kg) for seven days. Groups 6-8 were fed on food mixed with the same three doses of melamine formaldehyde for 7 days. Groups 9-11 treated orally with melamine formaldehyde (0.88, 1.16, 3.2 mg/kg) for 14 days. Groups 12-14 were fed on food mixed with the same three doses of melamine formaldehyde for 14 days. Liver enzymes and kidney functions were affected and malondialdehyde (MDA) content, glutathione peroxidase (GPx) and acetyl cholinesterase activities in brain was altered by the melamine. The histological examination of liver of melamine showed many degenerative changes including cytoplasmic vacuolization of the hepatocytes, fatty infiltrations, leucocytic infiltrations, congestion of blood vessels and fibrosis and kidney necrosis, atrophy some glomerular and tubular epithelium. Chromosomal aberration showed fragmentation, polyploidy, breaking gaps, deletion, and multiple aberrations. In conclusions, melamine should be absent from diet at milligram concentrations to safe our health.