We report on the growth behavior of high-quality GaN epilayers via GaN nanowires (NWs) assisted epitaxial lateral overgrowth (NWELOG) by using metalorganic chemical vapor deposition (MOCVD). Initially, an array of well-aligned GaN NWs were grown on Si(111) substrates via vapor-liquid-solid (VLS) method and then the successive lateral overgrowth of GaN epilayers using 4 step NWELOG at the upper part of the NWs. A thickness of GaN epilayer of about 5 to 6 μm was achieved. Transmission electron microscopy (TEM) study revealed a significant reduction of the dislocation density at the laterally coalesced GaN epilayers. A comparative analysis of atomic force microscopy (AFM), photoluminescence (PL) and X-ray diffraction (XRD) data of the GaN epilayer between NWELOG and lateral epitaxy on patterned substrates (LEPS) revealed that the NWELOG grown GaN epilayers were superior. From the AFM analysis, there were no surface pits on the GaN epilayers grown by the NWELOG process. The strong PL emission peak was observed at 365 nm for the GaN epilayer on Si(111). These results demonstrate that the NWELOG technique can improve the quality of GaN epilayers on Si substrates without surface crack generation or any related defects. © 2012 The Royal Society of Chemistry.