Large dispersion in the peak position of the OH⁻ stretching mode (~687.9 and ~2167.7 cm⁻¹/eV for fundamental and 3rd harmonic, respectively) is observed by Resonance Raman studies in congruent lithium tantalate single crystal under varying excitation energies. This is explained by considering the involvement of multiple LO phonons in the interaction with OH⁻ stretching vibration and the resonantly excited electrons. The intensity of the peaks is also found to vary with the excitation energy. FWHM increases with the increase in excitation energy because of individual contributions of the increasing number of resonance steps to the broadening.