In this study, effects of small amount of methyl-polyhedral oligomeric silsesquioxanes (methyl-POSS) on the microstructure and isothermal melt-crystallization behavior of polyoxymethylene (POM) were investigated, in detail. Introducing of methyl-POSS particles in POM phase was achieved via melt blending of methyl-POSS reinforced isotactic polypropylene (i-PP) nanocomposite as POSS carrier material with POM in a twin screw co-rotating extruder. Microstructural features of the POM/PP-POSS compounds were investigated with scanning electron microscopy (SEM) analysis. SEM analysis showed that the POM/PP-POSS compounds exhibited immiscible blend morphology. The POM, continuous matrix, phase includes a significant number of POSS particles due to interfacial interactions between the Si-O bonds of POSS and C-O bonds of POM, and resulted POSS migration from PP to POM phase during the melt processing. The kinetic parameters for the isothermal melt-crystallization process of the samples were determined with the Avrami and Lauritzen-Hoffman models. The crystallization activation energies were determined by the Arrhenius method. It was found that the PP-POSS nanocomposite significantly accelerated the isothermal crystallization rate of POM. Based on the results, it has been highlighted that POM compounds including a small amount of PP-POSS nanocomposite as POSS carrier material can be successfully used in the production of injection molded POM parts because the POM/PP-POSS compounds yield much faster molding cycle thus production rate than the POM. (C) 2012 Elsevier Ltd. All rights reserved.