Herein,　a　strategy　is　proposed　for　the　self-assembly　hybrid　hierarchical　structure　of　a　WO3　nanosheets/W18O49　nanowires　(HHW)　composite　via　a　one-step　hydrothermal　method.　The　method　requires　only　H2O　and　surfactants　to　regulate　the　hydrolysis　rate　of　tungsten　ions　to　yield　the　desired　morphology.　The　self-assembled　growth　of　the　hierarchical　structures　is　principally　governed　by　the　competition　and　equilibrium　between　the　surfactant　concentration,　precipitation　coefficient,　and　hydrolysis　rate　of　tungsten　ions.　The　hybrid　hierarchical　HHW　material　exhibits　an　ultrahigh-sensitive　response,　up　to　1678　upon　exposure　to　10　ppm　of　NO2,　which　demonstrates　a　significant　enhancement　over　that　of　conventional　hierarchical　gas-sensitive　nanosheet　or　nanowire　materials.　The　ultrahigh-sensitive　response　and　excellent　selectivity　toward　NO2　by　HHW　is　considered　to　derive　from　the　synergistic　effect　of　rapid　electron　separation　and　transport　by　the　W18O49　nanowires　and　the　abundance　of　adsorption　sites　offered　by　the　WO3　nanosheets.　This　low-cost　and　rapid　synthesis　of　self-assembled　hybrid　hierarchical　materials　provides　an　effective　strategy　for　high-performance　gas　sensors　or　catalysts.