Mg-doped GaN films with a variety of Mg concentrations were grown on sapphire (0001) by horizontal atmospheric metalorganic chemical vapor deposition (MOCVD) system with three layered laminar flow gas injection in an attempt to study the Mg doping effects on film quality. The increase of Mg concentration induced an increase of x-ray rocking curve full width at half maximum (FWHM) and degradation of surface morphology. Secondary ion mass spectroscopy (SIMS) analysis shows increase of Si and O, associated with Mg-doping concentration. Si and O concentrations of Mg-doped film are up to 5×1016cm−3 and 5×1017cm−3 at Mg concentration of 4.5×1019cm−3, respectively. Strong 380nm emission and weak 430nm emission were observed by photoluminescence (PL) measurement at room temperature for as-grown Mg-doped GaN films which shows p-type conductivity after thermal annealing. While, in highliy Mg-doped GaN films which do not show the p-type conduction after thermal annealing, 430nm and/or 450nm emission were dominating. The highest room temperature free hole concentration achieved was p=2.5× 1018cm−3 with mobility μp=l.9cm2/V s.