Abstract: A total 14 vitamin algal extracts obtained from 7 strains (Dunaliella salina, Scenedasmus dimorphus (mutant), Chlorella (mutant), Scenedasmus dimorphus (normal), Chlorella (normal), Scenedasmus acutus (mutant) and Scenedasmus acutus (normal) grown under different environmental conditions, were tested for their ability to induce increased activity of the detoxifying enzyme system glutathione-S-transferase (GST) in several target tissues of female mice. In the normal algal extracts, increase of GST activity was ranged from 3 to 4.27, 1.99 to 2.77, 2.1 to 2.99 and 1.6 to 2.4 while the extracts obtained from the mutant algae, increase of GST activity was ranged from 4.29 to 6.79, 3.34 to 5.81, 3.64 to 4.37 and 2.31 to 3.19 times in the liver, small intestine, large intestine and lung, respectively as compared to control group. The vitamin extracts of D. salina were increased GST activity with 7.2, 6.21, 5.63 and 2.91 times than the control group in liver, small intestine, large intestine and lung tissues, respectively. Consequently, the vitamin extracts were evaluated to induce GST activity in different organs tissues of tumorous mice. The vitamin extracts of Dunaliella grown under stress conditions showed the most active extract that induced GST enzyme activity over all control groups including non-tumorous, tumorous (negative) and positive control groups (standard vitamins mixture). In liver, the GST activity was increased over the control groups by 8.12, 6.0 and 3.0, respectively. The data indicating that vitamin algal extracts were increase GST activity in tumorous tissues over than tumorous control group in all tissues examined suggested a correlation between the GST-induced ability in tumorous and inhibitory of tumorigeneses. Since, the ability to induce an increase in the detoxifying enzyme activity by natural compounds has been found to correlate with their activity in the inhibition of tumorigeneses. Therefore, algae extracts may be considered as a potential chemopreventive agent.