Abstract: In this paper the substituent effect in the electronic absorption spectra of cyanine dyes by means of the homologous linear equation has been studied.Its substituent effect is different from gerneral substituent effect, due to the presence of strong alternate phenomenon in the molecule of cyanine dyes.An empirical formula of wide applicability has been suggested and applied to Tarious types of cyanine dyes, including thiacarbocyanines, thiadicarbocyanines, thiatri-carbocyanines, selenacarbocyanines, selenadicarbocyanines and selenatricarbocyanines etc.and their derivatives.The wavelengths of the electronic absorption maximum have been calculated for more than one hundred compounds of cyanine dyes.The results indicate that about 70% of the total number of the compounds shows a deviation of ≤±5nm, about 25% with a deviation of ±5nm to ±10nm and about 5% with a deviation of greater than ±10nm.