Mixtures of poly(butylene terephthalate) (PET) and poly(ethylene terephthalate) (PET) polymers were formed using ball milling technique and characterized by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). PET with different degrees of crystallinity was used in the solid-state mechanical milling process. Results suggest that PET greatly influences the crystallization of amorphized PET by milling.