Higher Level of Fluoride in ground water is major concern in all over the world. In vivo genotoxicity investigation of the action of fluoride on bone marrow cells, Sodium fluoride was administrated through the drinking water to 6-8 weeks old Swiss albino mice for 7 days at 1 ppm, 2 ppm and 4 ppm Exposure of fluoride induce various types of chromosomal abnormalities were observed. The increase in frequency of chromosomal abnormality was due to significant increase in individual type (Chromatid breaks, Chromatid gaps, acentric fragment, minute fragment, Ring Chromosome) as well as Gross Type (Hypoploidy Polyploidy). The effect was dose descendent. This result indicates that the action of fluoride in vivo is more genotoxic at lower concentration (1 ppm) than at higher concentration (4 ppm).