Abstract: Reinforced rubber composites having high Young's modulus and tear energy and a highly improved creep strength are produced by melt-blending 100 parts by weight of a natural or synthetic rubber, 5-150 parts by weight of N-methoxymethylated nylon (degree of N-methoxymethylation: 10-40 mol%) in the presence of or in the absence of a filler and an antioxidant in Banbury mixer, mixing thereto 5-20 parts by weight based on 100 parts of said nylon, of a higher saturated aliphatic monobasic organic acid which is a cross-linking agent for N-methoxymethylated nylon, 0.5-20 parts by weight based on 100 parts of the rubber, of a cross-linking agent for rubber and an appropriate amount of compounding agents and simultaneously cross-linking the rubber and the N-methoxymethylated nylon.