In-plane c-axis oriented Ba-hexaferrite (BaM) thin films were prepared on a-plane sapphire (Al2O3) substrates using direct current (DC) magnetron sputtering followed by ex-situ annealing. The sputtering atmosphere was found to have a great influence on the stoichiometry, orientation growth, and grain morphology of the as-prepared BaM films. With moderate oxygen partial pressure during sputtering, in-plane c-axis highly oriented BaM films were obtained. The films showed strong magnetic anisotropy with a high hysteresis loop squareness (M-r/M-s of 0.96) along in-plane easy axis and a low M-r/M-s of 0.05 along in-plane hard axis. Rocking curves and pole figures were utilized to reveal the epitaxial-like orientation relationship of the BaM films relative to the sapphire substrates, as well as the orientation growth dispersion of the hexagonal platelet-shaped grains in BaM films.