Several unsolved problems experienced by our group were described. The first was concerned about the chemical reactivity of silica in rubber matrix. The oxidation reaction of polyisoprene was promoted by silica particle, however, this was not explained simply by ability of acid catalyst proposed for silica. The second was concerned about the destruction-reconstruction behavior of crosslinking structure by stretching. The broken structure partly recovered in the sample crosslinked by sulfur. However, such behavior was minor in the sample crosslinked by peroxide. The reason was uncertain. The third was stress-strain behavior of elastomer in relation to the changes of network structure. Although existence of inhomogeneous network structure should be taken into consideration, the details were not clear.