In this article, we study the evolution of networks based on natural rubber (NR) which is reinforced by in situ magnesium dimethacrylate (MDMA) during curing at a molecular level. The crosslink density of the compounds cured for different time was evaluated by a dissolution/swell experiment. The curing process was analyzed by using a UR-2030 Rotorless Rheometer. Mechanical properties of the composites cured for different time were also used to evaluate the evolution of the networks. The results reveal that the ionic crosslinks, cooperating with some primary covalent crosslinks and some other physical crosslinks, play an important role in supporting the crosslinked backbone of the composite to bear the external force in the initial curing time. The evolution of crosslinked networks could be divided into three regions in this particular experiment: network forming period dominated by the ionic bonds, fundamental network forming period, and ionic bonds rupture period. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012