Zinc oxide (ZnO) thin films deposited by DC magnetron sputtering were annealed in nitrogen atmosphere at different temperatures ranging from 100 to 500 degrees C with a step of 100 degrees C; the annealing time was 6 h. In order to study the film's crystallization kinetic, their structures were monitored by means of X-ray diffraction (XRD) analysis each hour. Variation in grain size, calculated from the XRD patterns, with annealing time and temperature, obeys the classical parabolic law of grain growth. Exponent n was found to be dependent on the annealing temperature; it ranged from 5.13 to 3.8 with increase in annealing temperature. From the obtained exponent n values we inferred that the grain growth mechanism is mainly governed by the atom jumping across the grain boundary. We have found that the grain growth is characterized by a low activation energy ranging from 22 to 24 kJ/mol. (C) 2010 Elsevier B.V. All rights reserved.