It is well known that the crystallization of polymers can be accelerated by the molecular orientation. Crystallization rate of poly(ethylene terephthalate) (PET) in the high-speed melt spinning process was evaluated through the on-line measurement of the spin-line. Crystallization rate analyzed based on the detection of the heat of crystallization was more than 10,000 times higher in comparison with that in the quiescent state. In this research, crystallization rate of PET and poly(L-lactic acid) fibers and films in an oriented amorphous state was evaluated utilizing the high-seed DSC. Measurement of the original fibers and films was not possible because of the disturbance of the measurement caused by the shrinkage of the samples during the heating process. Therefore, for both PET and PLA samples, pre-heat treatment of short time was applied so as to shrink the samples without crystallization. Evaluated crystallization rate for PET was found to be about 1000 times higher than the quiescent state even after the application of shrinking and orientation relaxation procedure. Similar analysis was conducted for PLA fibers. Surprisingly, both cold crystallization and melting temperatures for oriented amorphous PLA fibers increased with the increase of heating rate. This peculiar behavior was investigated in detail, and so far it was confirmed that there is no experimental flaw for the delayed phase transition with the heating rate.