A biodegradable crystalline aliphatic polyester, poly­(butylene succinate) (PBS), and an amorphous semiaromatic nylon, poly­(hexamethylene isophthalamide-co-terephthalamide) (PA6IcoT), were melted and reactively blended with p-toluene sulfonic acid as the catalyst. The isothermal and nonisothermal crystallization processes of PBS and its blends with PA6IcoT were investigated by differential scanning calorimetry (DSC). Three different models (Jeziorny’s, Ozawa’s, and Mo et al.’s methods) were used to simulate the isothermal and nonisothermal crystallization kinetics. Moreover, the crystalline morphologies were observed by polarized optical microscopy. The effects of PA6IcoT and the ester–amide exchange reaction between polyester and polyamide on the crystallization processes and crystalline morphology are described in detail.