Abstract: Three newly synthesized tetrahydronaphthalenthiazol derivatives I, II and III were examined to elucidate their antitumor activity against Ehrlich’s ascites carcinoma cells (EATCs) bearing mice through monitoring the tumor volume and life span of the mice. All the three compounds showed high antitumor potential in simultaneous treatment than the groups in which treatment was started 10 days post tumor inoculation especially compound III which showed highest activity on reduction tumor volume (from 6.00±0.46 to 2.10±0.18 CC) at 20 μg kg-1 b.w. in comparison to group treated with cisplatin which was used as a standard treatment drug and revealed reduction of tumor volume (from 6.00±0.46 to 0.50±0.04 CC) and also showed the most highest survival rate (34.50±2.70 days) with the increase of life span 67% at the same concentration compared to 74 and 0% in cisplatin and control groups, respectively. It is obviously from the present study that the tetrahydronaphthalenthiazol can possess antitumor activity and ameliorate and prolong the life span of mice bearing EATCs.