A designed MoO3/C nanobelts anode material for lithium ion batteries is obtained by a facile hydrothermal route in this work with (NH4)6Mo7O24·4H2O and activated carbon as starting materials. Owing to the polyporous structure of the activated carbon, molybdenum trioxide forms in the pores and then grows along the preferential orientation to build MoO3/C nanobelts, in which the MoO3 nanoparticles and carbon are dispersed uniformly and combined firmly. The synthesized material is studied in terms of structural, microstructural and electrochemical properties. The carbon component present in the composite serves as a physical barrier preventing the aggregation of the MoO3 nanoparticles, provides structural flexibility for accommodation of large volume changes on electrochemical cycling, and offers good electronic conductivity for electrode reaction, ensuring the observed vast improvement of the electrochemical properties of MoO3/C anode. The MoO3/carbon nanobelts with the designed microstructure exhibit a high specific capacity (up to 1000mAhg−1 after 50 cycles at a current density of 0.1Ag−1), superior rate capability (retaining a discharge capacity of 675mAhg−1 at a current density of 5Ag−1) and long-term cycle stability (to 550 cycles). In situ XRD examination on MoO3/C electrode is performed to understand the reaction mechanism of lithium with MoO3 in initial process.