From X-ray diffraction (XRD) measurements, long-range chemical ordering along the growth direction is observed in epitaxial(0001) CoxPt1-x (x similar to 0.8) alloy films. Such ordering increases with the deposition temperature up to 690 K, together with the volume fraction of hcp stacking sequence, and also depends on the crystalline quality of the epitaxial film. In contrast, no chemical order was detected in the (0001) planes. Digital processing of cross-sectional high-resolution transmission electron microscopy (HRTEM) images shows that a chemical order along the growth direction [111] also exists in the minority fcc phase of a Co82Pt18 film grown at 690 K.