The effects of the lattice misfit strain on the crystal system and the ferroelectric properties of BiFeO3 epitaxial thin films were investigated. The misfit strain was controlled by the introduction of a buffer layer. When the film thickness of BiFeO3 is 130 nm, the lattice parameter of the film was controlled by the lattice misfit. Furthermore, when the thickness is 900 nm, it was found that the crystal system of the film with misfit of -1.3 % was monoclinic, and that with a misfit of 0.5 % was rhombohedral. From the evaluation of the ferroelectric properties, it was found that the coercive electric field of the films with a misfit of 0.5 % was smaller than that with misfit of -1.3 %. Moreover, the polarization switching behavior and the leakage current at the microscopic region of the films were investigated using scanning probe microscopy. The results suggest that the lattice misfit causes the generation of defects in the grain and affects the polarization switching behavior.