STATEMENT OF PROBLEM Acrylic resin denture base resins are colonized by oral and nonoral bacteria and Candida species. This reservoir of microorganism causes denture stomatitis, which can be implicated in some life-threating infections in older denture wearers. PURPOSE The purpose of this in vitro study was to incorporate quaternized N,N-dimethylaminoethyl methacrylate (DMAEMA) monomer into a denture base resin and investigate its antimicrobial and mechanical properties. MATERIAL AND METHODS Quaternized ammonium monomer (QAM) was synthesized through the reaction of octyl bromide and DMAEMA. The synthesized QAM was incorporated into a denture base resin system (8 to 12 wt%). The resulting material was characterized by Fourier transform infrared spectroscopy. The in vitro antimicrobial property was determined by direct contact test against Escherichia coli, Staphylococcus aureus, and Candida albicans. Release of the QAM was also tested by means of an agar diffusion test. Mechanical properties were measured with a 3-point bend test, and results were analyzed and compared using ANOVA and the Tukey post hoc test (α=.05). RESULTS Spectroscopy confirmed the formation of quaternized ammonium modified denture base (QAMDB). The decrease in number of viable cells of E coli, S aureus, and C albicans was more than 99% for 12%-QAMDB in comparison with that of the control groups. An overall decline was observed in the flexural strength and flexural modulus of the fabricated resins (P<.05), but no differences were observed for strain at break or fracture work of the specimens (P>.05). CONCLUSIONS Denture base resins containing immobilized QAM provided high antibacterial activity, but the flexural strength and flexural modulus of the denture base resins decreased.