The ability to grow high-quality, single-crystal transition metal dichalcogenides (TMDCs) is important for the application of electronic and optoelectronic devices. Here, we report the epitaxial growth of highly-aligned molybdenum disulfide (MoS₂) on c-plane sapphire by chemical vapor deposition (CVD). The base edge of MoS₂ flakes is mainly along the [11−20] crystallographic orientation of c-plane sapphire. Structural characterization indicates that coupling between sapphire step edges and MoS₂ zigzag edges gives rise to epitaxial growth. We find that photoluminescence (PL) intensity of aligned MoS₂ is much weaker than that of randomly orientated MoS₂ flakes, attributing to the strong MoS₂-substrate interaction and thus introducing strain in aligned MoS₂. The ratio of sulfur and molybdenum trioxide (MoO₃) precursor in the CVD process also plays an essential role in the orientation of MoS₂ triangular flakes. In addition, the morphology of aligned MoS₂ flakes shows great growth temperature dependence and high growth temperature leads to the formation of trapezoid MoS₂ flakes.