In this paper, the effects of sintering additives B2O3 on sintering temperature, microstructure and transport properties of the Li7La3Zr2O12 (LLZ) ceramics prepared by solid state reaction are reported. The optimized conditions to synthesize the LLZ-xB(2)O(3) (x = 0.2-0.35)ceramics is 950 degrees C for 30 h with 10% excess lithium salt, which is nearly 300 degrees C lower than that by the conventional solid state reaction. Qualitative phase analysis by Xray powder diffraction patterns combined with the Rietveld method reveals garnet type compounds as major phases. Lithium ion conductivity of LLZ-0.3B(2)O(3) was studied by AC impedance method. LLZ-0.3B(2)O(3) ceramics exhibits the highest total ionic conductivity of 2.5 x 10(-4)S cm(-1) at room temperature. All solid state batteries consisting of Li/LLZ-0.3B(2)O(3)/mixture of LiMn2O4 and LLZ-0.3B(2)O(3)/LiMn2O4 cell exhibit the capacity of 102.6 mAh g(-1) at a current density of 5 mu Acm(-2) at the first discharge, which could run for 20 cycles with capacity retention of 94%.