A thermoplastic polyester resin includes a residue of an aromatic dicarboxylic acid or an ester-forming derivative thereof and a residue of a diol or an ester-forming derivative thereof, as main structural units, wherein the thermoplastic polyester resin has a hydroxy group concentration of 0.050 mmol/g or less. The use of such a thermoplastic polyester resin enables production of a molded article having excellent mechanical properties and heat resistance, and a reduced dielectric loss tangent at a high frequency of 1 GHz or more.