This article dealt with the relationship between mechanical properties and crosslinked networks of natural rubber (NR) reinforced by zinc dimethacrylate (ZDMA) after thermal aging. After thermal aging at the present experimental conditions, the covalent crosslink density showed a decrease all the time, whereas the ionic crosslink density was stable at 80 degrees C but decreased at a higher temperature. The decrease in the total crosslink density after aging indicates the degradation of the crosslinked network. However, an experimental phenomenon observed was that the tensile strength and tear strength increased in a certain degree after aging at 80 degrees C or at a 100 degrees C for a short time. In addition, the thermal stability of the NR/ZDMA composite was evaluated by thermal gravimetric analysis. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012