The present work is concerned with the effect of polystyrene (PS) content on the structure the double crystallization peaks of polyethylene terephthalate (PET) observed in PET/PS blends. Blends of PET and PS with 1% to 15% PS content (by weight) were compounded in a laboratory internal mixer as substantially amorphous materials, and the cold crystallization behavior studied by differential scanning calorimetry (DSC) conducted at 10C/min. The complex PET crystallization peak observed is often attributed to existence of multiple crystalline populations with different crystal stabilities. The complex peak was analyzed as the sum of two simple peaks, separated with the help of specialized software. While the total area under the complex peak (total crystallinity) is independent of PS content, the areas under the simple peaks (corresponding to the crystallinities of two different populations) are highly dependent on the amorphous component (PS) content, its proportion varying from 35:65 for 1%PS to 80:20 for 15%PS. Peak temperatures are in the range of 145-50C for the major peak and 130-135C for minor peak. The present contribution may be the basis for a quantitative interpretation of the dynamics of crystalline populations in PET/PS blends.