Uniaxial Co80Pt20 epitaxial films with in-plane anisotropy were prepared by dc sputter deposition using W/Ag templates on H-terminated Si(110) substrates. The epitaxial relationship as a function of the CoPt thickness, studied by electron and X-ray diffraction, is complex for CoPt thickness < 5 nm. For CoPt thickness > 5 nm, the epitaxial relationship was found to be CoPt(1010) || W(112) || Ag(110)|| Si(110). Anisotropy constants were measured using in-plane torque curves and the initial magnetization curves along the hard axis. For 10 to 20 nm thick Co80Pt20, Κ1 was found to be ~ 9 × 106 erg/cc and Κ2 was negligible.