Magnesium methacrylate (MD-MA) was in situ prepared in nitrile rubber (NBR) by reacting magnesium hydroxide (Mg (OH)(2)) with methacrylic acid (MAA) during the mixing step. The formation of MDMA in NBR was proved by the wide-angle X-ray diffraction analysis (WAXD). The mechanical properties, crosslinking structure, and morphology of the resulting peroxide-cured NBR vulcanizates were studied. Results showed that Mg (OH)(2)/MAA mixtures had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the ultimate properties. Both the covalent crosslink density and ionic crosslink density of the vulcanizates were measured. And the nano-composite morphology of such vulcanizates was also observed.