Distribution of nanoparticles in nanocomposites is one of the most important roles to design unique morphologies and properties; however, up to now, it is still very difficult to control distribution of nanoparticles in polymer matrix. Here we show a simple approach to fabricate ferroferric oxide (Fe3O4) nanoparticles with controllable chain-like distribution in poly(e-caprolactone) (PCL) by a magnetic self organization. Randomly distributed Fe3O4 nanoparticles can be polarized and the interparticle dipole dipole attraction drives their assembly into linear chains in an external magnetic field. The accelerated PCL crystallization happens at low Fe3O4 loadings, while the retardation to crystallization happens at high Fe3O4 loadings, especially for the samples with chain-like structures. Furthermore, PCL spherulites are also arranged into chain-like structures by the Fe3O4 nanoparticle chains. As a result, the PCL/Fe3O4 nanocomposites with chain-like structures exhibit higher storage modulus, Young's modulus and tensile strength than that of the corresponding nanocomposites with random distribution of Fe3O4 nano particles, indicating mechanical enhancements. (C) 2017 Elsevier Ltd. All rights reserved.