Thin films of poly(bisphenol A-co-decane) (BA-C10) were isothermally crystallized at different temperatures. The lamellar structures and branching during crystallization were observed in real time at different temperatures by an atomic force microscope equipped with a high-temperature heater accessory. Our observations indicated that induced nuclei developed into subsidiary lamellae, forming lamellar branches. Lamellar branches occurred randomly on the parent lamellae at high degrees of supercooling. However, lamellar branches were seldom observed at crystallization temperatures near the melting point. The minimum induction time for induced nucleation was found to occur at around 55 degreesC.