The preparation of mesoporous carbon nitride (p-CN) structure by the selective dealloying process of Ni/a-CN nanocomposite films is investigated. The composition and structure of the Ni/a-CN nanocomposite films and porous carbon nitride (p-CN) films are determined by scan electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Phase separated structure including nickel carbide phase and the surrounding amorphous carbon nitride (a-CN) matrix are detected for the as-deposited films. Though the bulk diffusion is introduced in the film during the annealing process, the grain sizes for the post-annealed films are around 10 nm and change little comparing with the ones of the as-deposited films, which is associated with the thermostability of the CN surrounding in the film. The p-CN skeleton with its pore size around 12.5 nm is formed by etching the post-annealed films, indicative of the stability of the phase separated structure during the annealing process. (C) 2018 Elsevier B.V. All rights reserved.