Hierarchical heterostructures consisting of W₁₈O₄₉ nanowires grown on CuO nanowires have been prepared and studied for their gas sensing properties. SEM images show that W₁₈O₄₉ initially grow as an shell over core CuO nanowire with protusion like branches whose thickness depends on oxygen partial pressure. These CuO:W₁₈O₄₉ structures were dielectrophoretically isolated and studied for their gas sensing properties. The results show potential of use of tailored hierarchical heterostructures for the fabrication of gas sensors.