Single-phase (0001) hexagonal boron nitride (h-BN) heteroepitaxial layers were successfully grown on lattice-matched Ni (111) substrate by flow-rate modulation epitaxy (FME) using triethylboron (TEB) and ammonia (NH 3 ) at 1020°C for the first time. The structural properties of the h-BN layers were investigated by high-resolution X-ray diffraction (XRD). The first-ever X-ray rocking curve (XRC) measurement of an h-BN layers was performed and the minimum full-width of half-maximum of 0.7° was obtained. For the h-BN FME growth, larger NH 3 flow rates and longer NH 3 exposure time are preferable for improving the crystal quality. Our approach enables us to drastically improve the crystal quality of h-BN at relatively low growth temperature.