The morphology change of oxide precipitates from platelet to polyhedron has been studied with high temperature annealing at 1100 degrees C from 1 to 16 h, after preannealing at 900 degrees C from 1 to 64 h. The following findings have been obtained by transmission electron microscopy observations. (i) Three types of polyhedral precipitates were formed after high temperature annealing depending on the preannealing time. They were an isolated polyhedraon without dislocations observed after preannealing for 1 and 4 h, an isolated polyhedron with dislocations observed after preannealing for 4 and 16 h, and an aggregation of polyhedra with dislocations observed after preannealing for 64 h. (ii) The change in shape of the precipitate from platelet to isolated polyhedron is delayed with preannealing time. (iii) The observed dislocations were generated during preannealing around the platelet precipitates.