Abstract Hydrogels have drawn considerable attention in the field of flexible chemical sensors due to their unique 3D structure, high permeability, ion‐conductivity, and tissue‐like mechanical properties. These structures and properties allow them to be functionalized into diverse sensing components and respond to chemical signals in complex environments. Herein, an overview of functional hydrogel‐based flexible chemical sensors is provided. First, the representative hydrogel materials are introduced and the operating principles for flexible chemical sensors are discussed. Then, state‐of‐the‐art functional hydrogel‐based flexible chemical sensing applications are highlighted including gas sensors, humidity sensors, pH sensors, glucose sensors, wound monitoring, and others. Finally, major challenges and opportunities in this field are provided.