To investigate how the Molecular weight of poly(ether ether ketone) affected the crystallization behavior, the nucleophilic reaction synthetic technology was used to obtain poly(ether ether ketone) of different molecular weights and the trend of the molecular weight varying with the duration of the reaction. Furthermore, the influence molecular weight has brought to the morphology and the melting behavior was investigated by means of FTIR, OM, WAXD, and DSC and thoroughly discussed in theory. Results showed that with the increase of the molecular weight, the degree of crystalline perfection and the lamellar thickness descended as well as the radius of spherulite diminished due to the difficulty of the chain mobility. Moreover, the melting temperature mounted up at first then decreased with the growing of the molecular weight indicating how the lamellar thickness and the melting heat per unit volume affected the melting behavior together. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2060-2070, 2009