Abstract: The reaction mechanism of LiX(X=H,D,T) with H₂O was investigated at MP2/6-311G(d) level using ab initio quantum chemistry in Gaussian03 software. The equilibrium geometries, harmonic frequencies and energy of various stationary points on the potential energy surfaces were calculated in the lowest singlet states. Considering the quantum correction, the reaction rate constants were calculated using classical transition state theory. The results show the reaction of LiH(LiD, LiT) with H₂O was considerably dependent on temperature that it is lower, the reaction rate constants are smaller.