Mixed lithium/ammonium perchlorate, Li(0.41)(NH4)(0.59)ClO4, has been prepared by gel diffusion using agar agar gel as the medium of growth at ambient temperature. The Cl and mixed Li/N atoms are located on the 4a (½, ½, ½) and 4b (½, 0, ¼) special positions, respectively, in the space group I42d. The structure features a twofold interpenetrated three-dimensional entanglement architecture, in which single three-dimensional networks are constructed from tetrahedral coordination based on [-(ClO4)-(Li/NH4)-(ClO4)-]∞ diamondoid arrays. A comparison of the crystal structures of Li(0.41)(NH4)(0.59)ClO4, LiClO4·3H2O, LiClO4 and NH4ClO4 is given.