Abstract: The Solvent effect on absorption spectra and laser induced emission fluorescence spectra of 16 cyanine dyes in 18 solvents has been studied. The results show that the shift of absorption peak Δσ_A and the energy difference (σ_A-ν_F) depend not only on the refractive index of the solvent used, but also on its dielectric constant. Therefore, tne new functions f(n,ε)=(n~2-1/2n~1+1)+α(ε-1/ε+2) and f(n,ε)=(ε-1/2ε+1)-(n~2-1/2n~2+1) are used instead of the Bayliss function f(n)=(n~2-1/2n~2+1) for absorption and fluorescence respectively. The effect of sovlent polarity on the position and intensity of the fluorescence peak and the order of ~1(n, π~*) and ~1(π, π~*) states of these dyes has also been studied in this work.