The thermal annealing behavior of oxygen in neutron irradiation Czochralski-silicon (CZ-Si) has been investigated systemically. It was found that a heavy dose of neutron irradiation accelerated the oxygen precipitation in CZ-Si under higher annealing temperature (1070-1130degreesC). We attribute this effect to the form of defect cluster induced by neutron irradiation, it may be as the core for the oxygen precipitation heterogeneous nuclei and those shorten the nucleation time and accelerate oxygen precipitates in the bulk of Si wafer. In addition, the oxygen diffusion is enhanced by the presence of a large quantity of vacancies near the surface of the wafer. (C) 2003 Elsevier Science B.V. All rights reserved.