By reacting esterification of phenolphtalein with methacrylate chloride, phenolphtalein dimethacrylate was obtained. Based on the results of elemental analysis, FTIR, H-1-NMR and C-13-NMR spectra, the structure of the product was proposed. The dimethacrylate was used as new crosslinker to crosslink poly(methyl methacrylate) (PMMA). The influence of the amount dimethacrylate on the crosslink density and some properties of the crosslinked polymers networks such as swelling, mechanical properties (tensile strength and elongation at break) and thermal stability were examined.