A simple method was proposed to prepare carbon nanotubes (CNTs) with uniform diameter and controlled wall number. Concentric graphene layers were homogeneously deposited on CNTs by aerosol-assisted chemical vapor deposition. The formation of new concentric graphitic layers on the pristine CNTs was linearly proportional with the deposition time, resulting from a competition between the dehydrogenation of hydrocarbons and the hydrogenation of the deposited carbon atoms on the CNT surface. This process homogeneously thickens the CNT diameter by increasing their wall number, allowing an accurate control of the CNT morphology, which is of great interest in a wide range of applications.