The morphology of the microcellular ethylene-propylene-diene terpolymer (EPDM) vulcanizes of both an unfilled and filled compound was studied from SEM photomicrographs. Carbon blacks adversely affect the average cell size, maximum cell size, and cell density. Enclosed gas pressure in a dosed cell increases the relative modulus at higher strain. Tensile strength decreases more steeply than the expected value obeying the additive rule. At higher temperature, tensile strength, elongation at break, and modulus values decrease. The stress-relaxation behavior is independent of blowing agent loading, i.e., the density of closed-cell microcellular rubber. The elastic nature of the closed cell, i.e., the gas bubble in the microcellular rubber, reduces the hysteresis loss compared to solid rubber vulcanizates. Theoretically calculated flaw sizes are found to be about 3.4 times larger than the maximum cell sizes observed from SEM photomicrographs. It reveals that tear path deviates from the linear front and gives an effective larger depth of the flaws.