To improve the safety concerns of lithium-ion batteries, a flexible scalable composite electrolyte film (FSCEF) was fabricated based on a fiber-shaped ceramic and polymer support. Ceramic fibers of Li_1.3Ti_1.7Al_0.3(PO₄)₃ (LATP) were prepared by sintering the precursor-coated sacrificial template and then infiltrated with a polyethylene oxide (PEO) polymer to obtain the FSCEF. The LATP fibers induced continuous Li⁺ ion channels, allowing the FSCEF to show an ionic conductivity exceeding 10⁻⁴ S cm⁻¹ at 60 °C. The synergistic action of the ceramic frameworks and supportive PEO resulted in enhanced mechanical flexibility. Furthermore, the possibility of using a FSCEF in all-solid-state batteries was confirmed by conducting electrochemical performance tests on a Li/FSCEF/LCO (LiCoO₂) cell. We expect that the herein reported findings will contribute to the synthesis of thin and flexible solid-state electrolyte films with manufacturing scalability for promising high-voltage all-solid-state batteries.