A resin composition characterized as containing (A) a synthetic resin having a melting temperature of 300° C. or above and (B) a platy inorganic filler incorporated in the resin and having the following properties;pH of aqueous dispersion: 5.5-8.0,amount of extracted alkalis: Na 30 ppm or below and K 40 ppm or below,maximum diameter a: 50 μm or below,thickness b: 1.0 μm or below, andaspect ratio (a/b): 20 or above.