We report the growth of A1N epilayers on c-plane sapphire substrates by pulsed metal organic chemical vapor deposition (MOCVD).The sources of trimethylaluminium (TMAl) and ammonia were pulse introduced into the reactor to avoid the occurrence of the parasitic reaction.Through adjusting the duty cycle ratio of TMAl to ammonia from 0.8 to 3.0,the growth rate of AlN epilayers could be controlled in the range of 0.24 m/h to 0.93 m/h.The high-resolution x-ray diffraction (HRXRD) measurement showed that the full width at half maximum (FWHM) of the (0002) and (10-12) reflections for a sample would be 194 arcsec and 421 arcsec,respectively.The step-flow growth mode was observed in the sample with the atomic level flat surface steps,in which a root-mean-square (RMS) roughness was lower to 0.2 nm as tested by atomic force microscope (AFM).The growth process of AlN epilayers was discussed in terms of crystalline quality,surface morphology,and residual stress.