W-doped Li7La3Zr2O12 electrolytes with composition of Li7-2xLa3Zr2-xWxO12 (LLZWO, x=0-0.55) were prepared by conventional solid state reaction. The incorporation of W proves beneficial to stabilization of cubic phase and densification of the ceramic, resulting in relative density of 96% and ionic conductivity of 6.6×10−4 Scm−1 at 25°C. Further analysis indicates that the LLZWO is not only chemically but also electrochemically (at least up to 4.5V) stable against Li metal anodes. The batteries consisting of Li/LLZWO/Electrolyte-soaked separator/LiNi0.33Mn0.33Co0.33O2 at 25°C exhibit the capacity of 142mAhg−1 at a constant current of 15mAg−1 at the first discharge, which could run for 20 cycles with capacity retention of 94%. These results indicate that the W-doped LLZO ceramics are promising electrolytes for solid state lithium ion batteries.