In order to study the feasibility of porous layer supported all-solid state battery, mechanical properties including flexural strength, Young’s modulus, and hardness of Li₇La_2.75Ca_0.25Zr_1.75Nb_0.25O₁₂ (LLCZN) were studied. The flexural strength of LLCZN with varies porosity and grain size was determined based on ASTM C1161. Young’s modulus and hardness was obtained through nanoindentation technique. The flexural strength of LLCZN with full density is ~150 MPa. The refinement of the grain size can further increase the flexural strength. The dense LLCZN garnet has a Young’s modulus of ~147.2±6.6 GPa and a hardness of ~13.9±1.4 GPa. Above results indicate that the LLCZN garnet has sufficient strength, stiffness, and hardness as the dense layer in a porous layer supported all-solid state battery.