Exploring high-capacity electrode materials is critical for the development of K-ion batteries. In this work, we report a layered-structured tungsten selenide (WSe₂) anode, which not only delivers an ultrahigh volumetric capacity of 1772.8 Ah/L (or 188.4 mAh/g) at a current density of 5 mA/g but also exhibits good rate capability (72 mAh/g at 200 mA/g) and cycling stability (83.14% capacity retention over 100 cycles at 100 mA/g). We have also revealed the underlying reaction mechanism through ex situ X-ray powder diffraction. Furthermore, proof-of-concept full-cell batteries comprising of WSe₂ anodes and Prussian Blue cathodes are capable of delivering an energy density of 135.2 Wh/kg_{cathode+anode}. This work highlights the potential of WSe₂ as a promising high-volumetric-capacity anode material for rechargeable potassium-ion batteries.