We present a high temperature heat treatment study of CVD-grown graphene nanoribbons annealed up to 2800 degrees C, demonstrating a progressive annihilation of lattice defects as the heat treatment temperature is raised. Starting at 1500 degrees C, single and multiple loop formation were observed on the ribbons edges as the temperature was increased. The structural changes of the samples are documented by X-ray diffraction, Raman spectroscopy, TGA, SEM, and HRTEM. This work indicates that nanoribbon annealing eventually leads to defect-free samples, through graphitization and edge loop formation. The annealed material exhibits structural differences that could be tailored for a variety of specific applications. (C) 2009 Elsevier B. V. All rights reserved.