The position of proton inside manganese dioxide, γ-MnO2, was studied by the total neutron-scattering technique using H/D isotopic substitution. The first-order difference was obtained by subtracting the results for the two different isotopic compositions and obtaining the weighted sum of partial structure factors and radial distribution functions related to the structure around hydrogens. The deuterium-substituted γ-MnO2 was prepared by de-intercalation of the proton via an oxidative treatment prior to re-intercalation with deuterium. The proton occupied two different positions with the H-O length of 1.0 and 1.9 Å, which corresponds to the 'Ruetschi' and 'Coleman' protons, respectively. The former protons situated in the Mn4+ vacant site and the latter in the tunnel centered in an oxygen octahedron. The isotopic substitution technique and the structure around protons are discussed in details. © 2007 Elsevier Inc. All rights reserved.