Optical transmission spectra of single crystal 0.24Pb(In1/2Nb1/2)O-3-(0.76-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3)(x = 0.27, 0.33) were measured in the pseudo-cubic crystallographic directions [111] and [112]. Ferroelectric domain structures were observed in order to explain the difference of transmittance for the two composition crystals. Wavelength dependence of the absorption coefficients was measured and the optical energy band gaps were calculated for both direct and indirect transitions, which are E (gd) = 3.09-3.18 eV and E (gi) = 2.89-2.96 eV, respectively, and the phonon energy is E (p) = 0.07-0.08 eV. The transmission spectra were explained by the refractive indices and extinction coefficients measured by spectroscopic ellipsometry.