PbTiO3 thin films grown on (001)MgO and (110)MgO by MOCVD have been characterized by x-ray diffraction and transmission electron microscopy. The PbTiO3 films deposited on (001)MgO under the optimum conditions always show a bi-layer structure. The top layer of the films near the free surface is c-axis oriented with the orientation relationship (001)PbTiO3∥(001)MgO. The bottom layer of the films near the substrate is a-axis oriented with (100)PbTiO3∥(001)MgO. 90° domains were observed, but only in the caxis oriented layers. The thickness of the a-axis oriented layers near the substrate decreases with decreasing the cooling rate. PbTiO3 films deposited on (110) MgO, however, are single-layer, epitaxial films with (101)PbTiO3∥(110)MgO.