Facile synthesis of various thienylazo-thiazole and thienylazo-thiophene dyes were described. 2-Amino-5-(2-thienylazo)-thiazole dyes 5 and 6 have been constructed by coupling the diazotized 2-aminothiophenes 1a and/or 1b with 2-amino-4-phenylthiazole (3) and/or 2-(N-methylamino)-4-phenylthiazole (4). Coupling of 2-aminothiophene derivative 1a with 2-acetyl-3-oxo-N-phenylbutanethioamide (7) affected cleavage of one acetyl group to furnish the corresponding 2-acetyl-2-thienylazo-thioacetanilide dye 8 which has been utilized as a precursor for the construction of different 3-methyl-2-substituted-4-thienylazo-thiophenes 10-13 through its treatment with the appropriate alpha-chlorinated reagents (namely; MeCOCH2Cl, PhCOCH2Cl, ClCH2COOEt and ClCH2CN). The effect of solvent polarity on absorption spectra was investigated, as was the relationship between dye structures and absorption in the UV–visible region.