There is provided a polyester resin including: moieties of dicarboxylic acid components including terephthalic acid; and moieties of diol components including 5 to 60 mole % of isosorbide, 10 to 80 mole % of a cyclohexanedimethanol, and the balance of other diol compounds, wherein the polyester resin has an intrinsic viscosity of 0.5 to 1.0 dl/g, and a melt viscosity of the polyester resin measured at a temperature of 280° C. and at a shear rate of 300 rad/s is at least 50% lower than that measured at a temperature of 280° C. and a shear rate of 1 rad/s, and there is also provided a method for preparing the polyester resin, including: esterifying diol components including 5 to 60 mole % of isosorbide, 10 to 80 mole % of a cyclohexanedimethanol, and the balance of other diol compounds, with dicarboxylic acid components including terephthalic acid in the presence of an esterification reaction catalyst including a zinc compound; adding a phosphorus-based stabilizer to the esterification reaction mixture at the time when the degree of esterification reaches at least 80%; and subjecting the esterification reaction product to polycondensation.