Four series of 5-amino-2-ethylmercapto-4-phenyl-6-subistitutedthieno[2,3-d]pyrimidine (8a-d), 4-chloro-7-ethylmercapto-9-phenylpyrimido[5',4':4,5]thieno[3,2-d]triazine (9) and 2-ethylmercapto-8-oxo-4-phenyl-7-(4-chlorophenyl)pyrimido [4',5':4,5]thieno[2,3-d]pyrimidine (10) were synthesized and their structures were confirmed by 1H NMR, 13C NMR and MS spectrum. All compounds were evaluated for the IC50 values against three cancer cell lines (MCF-7, HUH-7 and BHK) and WISH cell. The IC50 of compound (8d) was calculated for each cell line. Interestingly, the IC50 for the normal human amnion WISH cell line was much higher (723 μg/ml) than those found for tumor cell lines; for BHK (17 μg/ml), for HUH-7 (5.8μg/ml), and for MCF-7 (8.3 μg/ml). The proliferation inhibition of normal (WISH) and tumor (BHK, HUH-7, and MCF-7) cells by compound (8d) was investigated using MTT assay and IC50 was calculated after 48 hrs of treatment for each cell line.