The basic morphology of phase-separated VO2 films, in which the tetragonal (metallic) phase coexists with the monoclinic (insulating) phase, was studied using transmission electron microscopy. While the phase transformation temperature in an unstrained crystal is approximately 340 K, it was observed that at 298 K, elastic strain (caused by lattice mismatch with the TiO2-(001) substrate) stabilized the tetragonal phase near the VO2/TiO2 boundary. The observed zig-zag-shaped interface of the tetragonal phase was explained by the crystallographic orientation relationship between the tetragonal and monoclinic phases. The observations provide valuable information for future applications of VO2 films.