A portable water-activated power generating device, comprising a first supporting structure, a second supporting structure, a first electrode plate, a second electrode plate, a water-absorbent sheet, and a soft container. The second electrode plate has a first surface and a second surface opposite the first surface, and the water-absorbent sheet surrounds the second electrode plate and is in contact with the first surface and the second surface. The soft container is used for accommodating the second electrode plate and the water-absorbent sheet. The first electrode plate and the soft container are disposed between the first supporting structure and the second supporting structure.