We report the unique assembling behavior of Ag NP supported CNT nanocomposites. Initially Ag NPs were precipitated homogeneously on the walls of SDS-coated CNTs by a NaBH4 chemical reduction and/or photoreduction directly in an aqueous solution. An additional Ag source was subsequently added into the Ag-CNT dispersion and Ag was further reduced using hydroxylamine in a weakly alkaline condition. The morphology of the resulting Ag-CNT nanocomposites strongly depended on the Ag+ ion concentration. Interestingly, an anisotropic polyhedral self-assembly of Ag-CNT nanocomposites was observed when the Ag concentration was increased to 0.1 M (real concentration).