A foaming ethylene propylene diene terpolymer (EPDM) water-swellable rubber (WSR) was prepared using the multicomponent mechanical blending technology. The morphology of unfilled and silica-filled foaming EPDM WSR was studied from micrographs. The average cell size, maximum cell size, and cell density of the foaming WSR had a peak value with a 4-phr foaming agent loading in both unfilled and silica-filled WSR. The addition of silica made the average cell size and maximum cell size decrease and the cell uniform. With incorporation of silica, the tensile strength of the unfoaming WSR increased three times, while that of the foaming WSR increased about six times before immersing it into water. After water-swelling, the mechanical properties of both the unfilled WSR and silica-filled unfoaming WSR decreased, but that of the silica-filled foaming WSR increased. The silica filler accelerated the water-swelling rate and cut down the water-swelling equilibrium time at the same time. The foaming WSR had a better volume water-swelling ratio than that of the unfoaming WSR in both the unfilled and silica-filled WSR.