It is of great importance to develop low-temperature gas sensors for monitoring hydrazine (N2H4) with high toxicity and easy explosion. However, how to highly sense its ppb-level concentration remains challenging. For this purpose, biomorphic WO3 structure replicated by small-size nanoparticles was simply prepared though air calcinations of tungsten salt-immersed pine needle (PN) template. The mesoporous WO3-PN tubes with pore volume of 0.096 cc·g−1 had relatively large specific surface area (38 m2·g−1) for exposing more active sites, as well as rich oxygen vacancies (g = 2.005) and small band gap for promoting electron migration. With the assistance of W6+ Lewis acid catalytic sites, such unique multilevel structure facilitated the rapid transport and adsorption of basic N2H4 molecules, as well as their chemical reactions with high content of oxygen species (37.4 %) in sensing layer, thus first achieving the highly sensitive detection of ppb-level N2H4 gas at near room temperature. At 50 °C, WO3-PN sensor exhibited ultra-high response (S = 307), fast response time (Tres = 16 s) for 1 ppm N2H4, and low actual detection concentration (5 ppb). These key indicators were remarkably superior to reported semiconductor gas sensors. In addition, the enhanced low-temperature sensing mechanism of WO3-PN sensor was explored by means of analytical tests and DFT calculations.