Without a catalyst or template layer, GaN nanorods were successfully grown on c-sapphire substrates by RF-radical source metalorganic molecular beam epitaxy (RF-MOMBE). XRD, SEM, TEM, EDX and micro-PL were employed to characterize the structural and optical properties of GaN nanorods. The growth of GaN nanorods was uniformly observed across the substrate surface. These nanorods have an average diameter of 50 nm, and the rod number density can reach 1×1010 cm-2 depending on the growth parameters. The clear lattice fringes in HRTEM image revealed the growth of high quality hexagonal single-crystal GaN nanorods. and no droplet was observed at the end of the nanorods. Meanwhile, EDX analysis revealed that gallium and nitrogen as the only detectable elements. Room-temperature photoluminescence of GaN nonorods showed a band-edge-emission at the energy position of ∼3.4 eV. The catalyst-free growth mechanism of GaN nanorods was discussed on the basis of experimental results in this work. These high-quality and high-density GaN nanorods might be useful for practical applications in nanoscale optoelectronic and electronic devices.