To improve the characteristics of thermoplastic resin with high glass transition temperature; to provide resin composition for sheets producible at a low cost excelling in heat-resistance, mechanical characteristics, molding, and dimensional stability; and to provide a sheet for flexible printed wiring board reinforcement using the sheet and a flexible printed wiring board using it.

The sheet comprises thermoplastic resin 100 part by weight containing amorphous thermoplastic resin whose glass transition temperature is 230°C or more, and crystalline thermoplastic resin whose glass transition temperature is 130°C; and thermoplastic resin 5-50 part by weight containing tabular filler whose average particle diameter is 1-20 μm. The sheet for flexible printed wiring board reinforcement whose linear expansion coefficient is 45 ppm/°C or less and whose folding endurance (JIS P 8155: tension of 250 g, bending speed; 175 times per minute, bending side 0.38 R) is 5 times or more, and the flexible printed wiring board using it are provided.