In recent years, ionic polymer metal composites (IPMCs), as one important class of electroactive polymers (EAPs), have received tremendous interest for their potential applications in various sensing scenarios due to their softness, high sensitivity, inherent polarity, built-in actuation, and sensing capabilities, ability to work in water, and direct mechanosensory property. They also have bio-compatibility and amenability to microfabrication. This paper reviews the characteristics, sensing mechanisms, and typical sensing applications of IPMCs to provide references for interested researchers in related fields. The influences of different factors on IPMC sensor performance are also discussed.