A facile method is reported for the preparation of chain-like nanostructures by anisotropic self-assembly of TiO(2) and SnO(2) nanoparticles with the aid of a block copolymer in an aqueous medium. Well-defined crystallographic orientations between neighbouring nanoparticles are observed in TiO(2) nanochains, which is important for tailoring the grain boundaries and thus enhancing charge transport.