This work presents the first in situ observation of prefreezing as a mechanism of interface-induced crystallization in a molecular system. For this purpose, the crystallization and melting of thin epitaxial films of polyethylene (PE) and poly-ε-caprolactone (PCL) on graphite were studied with atomic force microscopy (AFM). During prefreezing, a thin crystalline layer is formed at the interface at temperatures above the melting temperature. This prefreezing layer was imaged with AFM measurements in the net-attractive regime of intermittent contact mode for both samples. The reversibility of the process, as well as an equilibrium layer thickness, was observed for PE on graphite. The PCL films allowed a direct measurement of the crystalline layer thickness, which shows a characteristic jump during formation, typical for prewetting layers. Hence, within the classical wetting theory, prefreezing is interpreted as the prewetting of the crystalline phase.