Owing to improved safety, all-solid-state batteries based on the garnet Ta-substituted Li7La3Zr2O12 solid electrolyte are promising alternatives to conventional Li-ion batteries with organic electrolytes. However, to date, the viability of such all-solid-state batteries is uncertain because their performance is limited by the problematic electrode-electrolyte interface. Herein, we report the viability to use Si anodes facilitated by enhancement of this interface. Before depositing Si as a thin film electrode (50 nm) on the smooth surface of the solid electrolyte, we treated the electrolyte surface by argon plasma etching to reduce the amount of resistive species. This approach enabled the cycling of Si/garnet/Li all-solid-state cells, achieving an initial capacity of ∼2700 mAh/g followed by partial fading and stabilization for more than 100 cycles. Electrochemical measurement, coupled with morphological and chemical investigations, demonstrate that Si is a viable anode in combination with garnet electrolyte and emphasize the importance of controlling the solid/solid interface.