A composition for forming a heat shrinkable film includes a polyethylene terephthalate (PET) resin having an inherent viscosity of 0.50 to 1.2 dl/g, and a polyester based copolymer including a dicarboxylic acid-derived residue including a residue derived from an aromatic dicarboxylic acid and a diol-derived residue including a residue derived from 4-(hydroxymethyl)cyclohexylmethyl 4′-(hydroxymethyl)cyclohexane carboxylate represented by the following Chemical Formula 1 and a residue derived from 4,4-(oxybis(methylene)bis)cyclohexane methanol represented by the following Chemical Formula 2.