This current study aimed at evaluating the toxic effect of nicotine and the possible protective role of green tea extract on some organs of Swiss albino mice by using histological, histomorphometerical and cytogenetical studies. Male Swiss albino mice were divided into four groups. The first group served as control and was injected intrapertoneally (i.p.) with distilled water (1ml DW/daily). The second group was injected with green tea extract (40 mg/ kg.b.w./i.p./ daily), animals of the third group were injected with nicotine (2.5 mg/kg.b.w./i.p. daily) and those of the fourth group were injected with nicotine (2.5 mg/kg.b.w./i.p/daily) and green tea extract (40 mg/ kg.b.w./i.p./daily). The experimental period was four successive weeks. Nicotine treatment induced histological changes in both the lung and testicular tissue as revealed by light microscope. It also induced histomorphological changes in the lung represent by significant decrease in elastic fibers and in the testicular tissue, a significant decrease in the number of Leydig cells. These changes were obtained by the computer image analyser. Combine administration of nicotine with green tea extract resulted in marked ameliorations of the testicular changes using histological and histomorphological observations. The combine administration of nicotine with green tea extract caused also an improvement in the ratio of PCEs/NCEs and a significant decrease in the increase of the MnPCEs numbers induced by nicotine treatment alone. In conclusions, the administration of green tea extract might suppress the cytotoxicity and mutagenic activity of nicotine. We suggest that green tea extract may be useful in combating tissue injury and genotocity caused by nicotine toxicity.