Novel styryl cyanine dyes and aza-styryl cyanine dyes having the nucleus of furo[(3,2-d)pyrazole;(3',2'-d)oxazole] iodide salt were prepared. Spectral sensitization evaluation for all the synthesized styryl and aza-styryl cyanine dyes was carried out through investigating their electronic visible absorption spectra in 95% ethanol solution. The dyes were thought to be better spectral sensitizers when they absorb light at longer wavelength bands (bathochromic shifted and/or red shifted dyes). Consequently the spectral sensitization of the dyes decreased when they absorb light at shorter wavelength bands (hypsochromic shifted and/or blue shifted dyes). The results discussed in this study revealed that the spectral sensitization properties of the examined dyes is highly effected by the type of the X substituted in the phenyl ring system for the styryl cyanine dyes and by the type of the phenyl and/or the naphthyl ring system for the aza-styryl cyanine dyes. Structural confirmations were identified by elemental analysis, visible spectra, IR and 1H NMR spectroscopic data.