The crystallization behavior of tetrakis [methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] methane (AO-60) in a chlorinated polyethylene (CPE) matrix was investigated. When the AO-60 content is 15 wt%, CPE/AO-60 is an incompatible system. The crystals on the surface of samples changed sequentially from a polyhedron shape to a platelet shape and then to a needle shape as the annealing temperature was reduced. The annealed samples showed two melting peaks. The high temperature peak is due to the melting of the AO-60 crystals observed. In contrast, in the case of a compatible CPE/AO-60 ( 5 wt%) system, AO-60 crystals also were observed but there was no change in the shape of crystals. The crystal growth of AO-60 within a CPE matrix is thought to depend on the compatibility of CPE/AO-60. (C) 2004 Kluwer Academic Publishers.