Ceramic–polymer composite electrolytes hold a great promise as next-generation electrolytes because of strong mechanical properties and wide electrochemical stability window. However, it remains challenges in improving ionic conductivity and lithium ion transference numbers. In this work, plasma treatment has been performed on Li 0.33 La 0.557 Ti 0.995 Al 0.005 O 3 (LLATO) nanofibers. The treated nanofibers are then incorporated with a polymer matrix to form a composite electrolyte. Plasma treatment has modulated oxygen vacancies, functional groups, polarity, and interfacial interaction of LLATO-polymer. This has improved lithium ion transport at interface of LLATO-polymer electrolyte. As a result, the LLATO-polymer electrolyte shows enhanced ionic conductivity and mechanical performance. This work has implication in design of ceramic-polymer composite electrolytes for solid state lithium metal batteries.