A membrane-electrode assembly for water electrolysis including a proton-exchange membrane, a first catalyst layer, a second catalyst layer, a first gas diffusion layer, a second gas diffusion layer and a first sensor chip. The proton-exchange membrane is disposed between an inner side of the first catalyst layer and an inner side of the second catalyst layer. The first gas diffusion layer is disposed on an outer side of the first catalyst layer. The second gas diffusion layer is disposed on an outer side of the second catalyst layer. The first sensor chip is sandwiched between the first catalyst layer and the first gas diffusion layer to sense an environmental change where water electrolysis takes place.