Acrylic resin is the dominant material that is broadly utilised to produce partial and complete dentures. The exposure of the denture-base acrylic resins to the oral environment as well as storing media for a certain period causes saliva sorption. In this study, composite materials-based polymethylmethacrylate (PMMA) reinforced with 1 wt% of glass fibres and (3, 6 and 9 wt%) yttrium oxide (Y2O3) have been prepared, and the addition influence upon some mechanical tests (tensile, flexural, hardness and surface roughness) has been investigated. Afterward, the mechanical properties of composite materials after immersion in artificial saliva for seven days have been evaluated. The results show that the Y2O3 percentage is 6%, which possesses a perfect feature. Thus, such a sample may be an encouraging material for achieving the needed properties for denture use. Furthermore, all mechanical properties were decreased after immersion in synthetic saliva.