A copolymerized polyamide resin includes a polymer of a monomer mixture comprising a dicarboxylic acid component comprising adipic acid and a dicarboxylic acid represented by Formula 1, wherein each R1 is independently a C1 to C5 alkyl group and a is an integer from 0 to 4, and a diamine component comprising m-xylene diamine and a diamine represented by Formula 2, wherein A is a single bond or a C1 to C10 hydrocarbon group, R2 and R3 are each independently a C1 to C5 alkyl group, and b and c are each independently an integer from 0 to 4, wherein the copolymerized polyamide resin has a difference between a melting temperature (Tm) and a crystallization temperature (Tc) of about 50° C. or more. The copolymerized polyamide resin may have excellent heat resistance and reduced or no gel generation and yellowing phenomenon in a molding process.