Form screening of thiazole group of compounds against various tumor cell line like HL60 and MCF-7, from results of MTT and XTT assay, It was found out that thiazole derivative potentially inhibits the proliferation of MCF-7 cells (human breast cancer) but not others cells like HL60 (human leukemia) and VERO (African monkey’s Kidney cell) presumably because of interaction of compounds with specific breast cancer cells. Initial screening was carried out by using MTT assay. Results obtained from MTT assay and XTT assay clearly indicates that out of 13 compounds only 6 compounds (2, 5, 8, 9, 10, and 13) show IC50 value below 100?M and that was against only MCF-7 cell lines where as against HL60 cell line, compounds did not show any sign of cytotoxicity. IC50 value of cyclophosphamide was 16.72 ?M against MCF-7 cell line by MTT assay, which was higher than compound no. 5 (14.13 ?M) and 13 (11.10 ?M). Confirmatory screening was carried out by using XTT assay in which all six compounds ware found to be effective against MCF-7 cell line but with higher IC50 values compared to MTT assay.