The present work provides improved recycled high molecular weight poly(ethylene terephthalate) (PET) by chain extension using 2,2'-(1,4-phenylene)bis(2-oxazoline) (PBO) as the chain extender. PBO is a very reactive compound toward macromolecules containing carboxyl end groups but not hydroxyl end groups. In the case of PET, where both species are present, for wen better results, phthalic anhydride (PA) was added in the initial sample, before the addition of PBO. With this technique, we succeeded in increasing the carboxyl groups by reacting PA with the hydroxyl terminals of the starting polymer. From this modification of the initial PET sample, PBO was proved an even more effective chain extender. So, starting from a recycled PET with intrinsic viscosity [eta] = 0.78, which would be [eta] = 0.69 after the aforementioned treatment without a chain extender or (M) over bar(n) = 19,800, we prepared a PET grade having [eta] = 0.85 or (M) over bar(n) = 25,600 within about 5 min.