A series of Thiazole Orange (TO) derivatives were synthesized and modified by introducing different substitutional groups on benzothiazole and 4-methylquinoline All the TO derivatives were confirmed by (1)HNMR and MS. TO derivative bearing NH(2)- was modified by folic acid and used to label breast cancer cells. The phenomenon of fluorescence enhancement was shown by the fluorescence spectrums of TO derivatives and micrographs of the labeled breast cancer cells. It offered a new try in the aspect of labeling cells by the embedded dyes.