A process for regenerating a polyester container, which comprises providing the polyester container provided with a polyester film comprising a copolymerized polyester resin comprising a diol component and a dicarboxylic acid component; crushing the container provided with the polyester film to obtain flakes; and thermally treating the flakes at 200°C to 220°C for 60 minutes to 120 minutes to produce regenerated polyester chips, wherein the copolymerized polyester resin comprises neopentyl glycol in an amount of 5 to 35% by mole based on the total number of moles of the diol component, wherein the step of providing the polyester container comprises covering the outer surface of the container with the polyester film; and having the polyester film shrunk by steam or hot air to wrap the outer surface of the container, wherein when a plurality of flakes are thermally treated at a temperature of 200°C to 220°C for 60 minutes to 120 minutes, the clumping fraction is 5% or less, wherein the flakes comprise first flakes obtained by crushing the container and second flakes obtained by crushing the polyester film, and wherein the heat shrinkable film has a heat shrinkage rate of 30% or more in the main shrinkage direction upon thermal treatment at a temperature of 80°C for 10 seconds when measured as indicated in the description, and a melting point of 170°C or higher as measured by differential scanning calorimetry while the temperature is raised at a rate of 10°C/min, wherein the clumping fraction is measured by passing the flakes through a sieve and thermally treating the flakes to form aggregates, passing said aggregates through a sieve again to be separated and then measuring the weight of the aggregates to calculate the weight ratio of the aggregates based on the total weight of the thermally treated flakes as the clumping fraction, wherein the crystallization temperature of the polyester film is not measured or is 70°C to 95°C by differential scanning calorimetry. crushing the container provided with the polyester film to obtain flakes; and thermally treating the flakes at 200°C to 220°C for 60 minutes to 120 minutes to produce regenerated polyester chips, wherein the copolymerized polyester resin comprises neopentyl glycol in an amount of 5 to 35% by mole based on the total number of moles of the diol component, wherein the step of providing the polyester container comprises covering the outer surface of the container with the polyester film; and having the polyester film shrunk by steam or hot air to wrap the outer surface of the container, wherein when a plurality of flakes are thermally treated at a temperature of 200°C to 220°C for 60 minutes to 120 minutes, the clumping fraction is 5% or less, wherein the flakes comprise first flakes obtained by crushing the container and second flakes obtained by crushing the polyester film, and wherein the heat shrinkable film has a heat shrinkage rate of 30% or more in the main shrinkage direction upon thermal treatment at a temperature of 80°C for 10 seconds when measured as indicated in the description, and a melting point of 170°C or higher as measured by differential scanning calorimetry while the temperature is raised at a rate of 10°C/min, wherein the clumping fraction is measured by passing the flakes through a sieve and thermally treating the flakes to form aggregates, passing said aggregates through a sieve again to be separated and then measuring the weight of the aggregates to calculate the weight ratio of the aggregates based on the total weight of the thermally treated flakes as the clumping fraction, wherein the crystallization temperature of the polyester film is not measured or is 70°C to 95°C by differential scanning calorimetry.