In this study, we investigated the anisotropic Li diffusion in Li10GeP2S12 using a molecular dynamics method. Although the calculated ion conductivity is slightly lower in comparison to the calculated and experimental ion conductivity of previous studies, our results support anisotropic Li diffusion. These findings show that the anisotropic Li diffusion estimated from the activation energy is an important property of Li10GeP2S12, and a potential factor for good ion conductivity. Further, a high diffusion coefficient was observed in Li10P3S12, which is a good Li-ion conductor.