Human skin is a stretchable sensor, which has inspired the development of mimics, with certain level of sophistication, to achieve wearable electronics. This rapidly growing field has currently received tremendous attention. Traditionally, “electronic skin” is generally considered as a stretchable sheet with sensitive sensors for various stimuli, including deformation, pressure, light and temperature. The sensors provide signal through stretchable electrical conductors like gold nanomeshes, silver nanowires and etc., which transmit signals via electrons. These “electronic skins” are limited in specific applications, such as biocompatibility in biometric sensor and transparency in tunable optics, although they meet the basic requirement of conductivity and stretchability. On the other side, the human skin report signals via ions. In this project, we explore the “ionic skin”, which has the potential in the development of a new type of sensory sheet that is highly stretchable, transparent, and biocompatible. The hydrogels, polymeric networks swollen with water, are highly stretchable and transparent ionic conductors. With combination of carrageenan and polyacrylamide, the double network hydrogel achieves extremely high stretchability, excellent transparency, and biocompatibility. The sodium chloride in water make the hydrogel as an excellent ion conductor. These double network ionic hydrogels are successfully fabricated as a strain sensor to monitor human motion. In addition, a highly stretchable, transparent ionic touch panel is also achieved.