Piezoelectric force microscopy is employed to study the ferroelectric domain structure in a 600 nm thick epitaxial BiFeO3 film. In the as-grown film, a mosaic-like domain structure is observed. Scans taken with the cantilever pointing along the principal crystallographic directions enabled us to reconstruct the polarization direction. By combining the perpendicular and in-plane piezoresponse data, we found that the ferroelectric domain structure is mainly described by four polarization directions. These directions point oppositely along two body diagonals, which form an angle of ∼ 71°. The other variants are also occasionally observed.