Ge-Doped Li_0.33La_0.56TiO₃ (Ge-LLTO) perovskites are synthesized with various GeO₂ contents by solid-state reactions as Li-ion conductive electrolytes for rechargeable all-solid-state Li batteries. After the addition of GeO₂, the sinterability and Li ion conductivity are enhanced for the perovskite solid electrolyte. The Li_0.43La_0.56Ti_0.95Ge_0.05O₃ electrolytes exhibit the highest sinterability and Li ion conductivity among the as-prepared Li_0.33+2xLa_0.56Ti_1−xGe_xO₃ electrolytes. The improvement of Li ion conductivity might be attributed to the improvement of the densification and structural integrity of the LLTO solid electrolyte. The lithium transference number (t_Li⁺) of Ge-doped LLTO is close to 1. Moreover, the Ge-LLTO electrolytes are stable in the potential range of 0–10 V vs. Li/Li⁺.