The present invention provides a resin composition enhanced in melt tension and remarkably improved in blow moldability without a parison being drawing down during blow molding, while being freed from the tendency to gelation at high viscosity, maintaining stable flowability and capable of effectively producing a blow molded article of comparatively large size having uniform thickness and excellent appearance.A resin composition for blow molding prepared by compounding 100 parts by weight of a resin component composed of:(A) 1 to 99 parts by weight of a thermoplastic polyester resin mainly comprising an aromatic dicarboxylic acid or the ester forming derivative thereof and an aliphatic dihydroxy compound having 2 to 8 carbon atoms and(B) 99 to 1 parts by weight of a thermoplastic polyamide resin with(C) 0.2 to 10 parts by weight of a styrenic copolymer comprising 40 to 97% by weight of styrene, 60 to 3% by weight of a glycidyl ester of an .alpha.,.beta.-unsaturated acid and 0 to 50% by weight of another vinylic monomer and(D) 0 to 100 parts by weight of at least one member among fibrous, granular and plate fillers and kneading the resulting mixture in a molten state.