Epitaxy between isotactic polystyrene (iPS) and isotactic poly(1-butene) (iPBu) has been studied. The epitaxial crystallization of iPS on the oriented form I iPBu film was realized through cold crystallization from its amorphous state at 130 degrees C for 10 h. The epitaxial crystallization of iPBu on the oriented iPS substrate induced initially by form I iPBu crystals, that is, the vice versa process, was achieved simply by heating the sample cold crystallized at 130 degrees C up to 190 degrees C to melt the iPBu crystals completely and followed by melt crystallization of iPBu. The results show that the epitaxy of iPS on iPBu form I crystals is based on two-dimensional lattice matching, which results in a parallel chain alignment of both polymers. On the other hand, the oriented iPS thin film produced by the form I iPBu ordered film in turn generates still a chain parallel epitaxy of iPBu but in its form II, even though the matching of iPS with form II iPBu is much poorer than with form I iPBu. This demonstrates that polymer epitaxy is not solely caused by geometric matching as widely accepted up to date. In the present case, the form II crystallization of iPBu on the iPS substrate is clearly controlled by the crystallization kinetics, while the chain orientation is associated with less pronounced one-dimensional lattice matching. These results shed more light toward a better understanding of polymer epitaxy.