Co₇₅Pt₂₅ (at. %) alloy thin films are prepared on MgO(111), SrTiO₃(111), and Al₂O₃(0001) single-crystal substrates by varying the substrate temperature from room temperature to 600 °C. Co-Pt epitaxial thin films with the close-packed plane parallel to the substrate surface are grown on these single-crystal substrates. The film structure is determined by considering the order degree and the atomic stacking sequence of close-packed plane. Metastable ordered phases of B_h and D0₁₉ are partially formed in A3 structure for the films grown on these single-crystal substrates at temperatures between 200 and 500 °C. Higher order degrees of 0.17, 0.26, and 0.19 are observed for the films grown at 300, 400, and 300 °C on MgO, SrTiO₃, and Al₂O₃ substrates, respectively. The ordered phase is preferentially formed around 300 °C. The films including the ordered phase show strong perpendicular magnetic properties reflecting the magnetocrystalline anisotropy of ordered crystal.