Formation energies of neutral and charged vacancies in lithium tantalate, as well as their electronic states have been investigated through first-principles calculations. It is found out that [Formula: see text], [Formula: see text] and [Formula: see text] are the most energy favorable vacancies on O, Li and Ta sites respectively. The formation energy of vacancy on the O site is lower in oxygen poor environments than that in oxygen rich environments, and the formation energy of vacancy on the cation site is lower in oxygen rich environments than that in oxygen poor environments. Among all types of neutral vacancies considered in this study, the energy of Li partial Schottky reaction, 2[Formula: see text] + [Formula: see text], is the lowest at almost all considered chemical environments. Taking into account the distribution of vacancy induced energy levels, we suggest that either [Formula: see text] or [Formula: see text] is responsible for the light absorption band around 460 nm observed in annealed LiTaO3 crystal.