A three-dimensional (3D) composite film containing copper nanostructures and carbon nanotubes (3DC/CNT composite film) was fabricated by one-step electrodeposition. The 3DC/CNT composite film was formed under galvanostatic conditions using a copper sulfate bath containing CNTs and polyacrylic acid which acts as both a 3DC-forming and a CNT-dispersing agent. The composite film consists of thin copper sheets with thicknesses of ca. 70-80 nm and CNTs, with large interior spaces between sheets. The CNTs were homogeneously distributed inside the composite film and were fixed by the copper sheets where CNTs pierce the copper sheets. The CNT content in the composite films increased with the CNT concentration of the plating bath. The 3DC film without CNTs did not maintain its 3D spaces when the film thickness was increased due to insufficient structural strength, whereas the 3DC/CNT composite film maintained the 3D spaces despite an increase in film thickness, which suggests that the CNTs reinforce the film to maintain the 3D spaces. (C) The Author(s) 2016. Published by ECS. All rights reserved.