WO3has different crystalline structures, including monoclinic and hexagonal phases. Monoclinic WO3(W-m) is the most common crystal phase in NH3-SCR catalysts. Hexagonal WO3(W-h) with empty hexagonal and trigonal tunnel structures exhibits excellent acidity and reducibility and can provide abundant catalytically active sites, but it is hardly applied in the NH3-SCR reaction. Herein, the effects of different WO3phases on the NH3-SCR performance of Ce-based catalysts are systematically investigated. The SCR activity of CeO2is both evidently improved by the addition of W-h and W-m. It is noteworthy that CeO2–WO3-hexagonal (Ce–W-h) exhibits a more excellent NOxremoval efficiency than CeO2–WO3-monoclinic (Ce–W-m) in the whole temperature window tested, and T50and T90of Ce–W-h are 51 and 111 °C lower than those of Ce–W-m, respectively. Importantly, compared with that of W-m, the special open structure of W-h not only facilitates NH3adsorption and the diffusion of oxygen to improve the acidity and reducibility of the catalyst, but also is favorable for electron transfer between W-h and Ce to boost the interaction between W-h and Ce. Besides, the active plane (001) on W-h/Ce–W-h can provide abundant unsaturated W6+and Brønsted acid sites. Accordingly, the Ce–W-h catalyst displays a more impressive NH3-SCR performance than Ce–W-m. W-h is a better choice to modify CeO2to improve its SCR performance than W-m. This work provides a profound understanding of the intrinsic effect of the crystal phases of WO3on NH3-SCR performance.