Optical properties of lanthanum-gallium tantalate crystals grown in different atmospheres (argon, argon-oxygen mixture, air) have been investigated. Optical transmission spectra in the ranges 0.185–0.800 and 2.0–10.0 μm have been recorded. The range of lanthanum gallium tantalate transparency is established to be 0.26–7.6 μm. The main refractive indices no and ne have been measured and their inhomogeneity and dispersion have been investigated in the range 0.40–0.70 μm. It is shown that the growth atmosphere significantly affects the optical properties of the crystals studied.