The microstructure of an epitaxial PbTiO3 thick film was investigated by using transmission electron microscopy (TEM). An analysis of bright-field TEM (BFTEM) images revealed the existence of displacements along the  direction of PbTiO3. High-resolution TEM (HRTEM) observation indicated that stacking faults parallel to the (001) plane of PbTiO3 are formed in the thick film. Local strain fields around the stacking faults were quantified by geometric phase analysis of the HRTEM image. The measured strain suggested the presence of a pair of extrinsic and intrinsic stacking faults. The distance between an extrinsic stacking fault and an intrinsic one corresponds to two unit cells along the  direction of PbTiO3. The formation of these stacking faults is considered to be associated with the strain relaxation of the film.