The aim: This study evaluates the effect of adding silanized halloysite nanotubes to the polymethylmethacrylate (PMMA) resin on its hardness, impact strength, transverse strength. Materials and methods: Three groups of acrylic resin were prepared, one group without HNTs, was used as a control group (A). The other two groups contained 0.3% (B), 0.6% wt of silanized halloysite nanotubes (C). For each one, hardness, impact strength and transverse strength were measured. One-way ANOVA and Tukey’s test were used for comparison. Results: Regarding to the impact test, there was no significant difference between 0.3% concentration and the pure (control) group while 0.6% concentration had significant decrease compared to the pure group and so between the 0.3% group 0.6% group. For the hardness test, the 0.3% group had no significant difference with the pure group and a significant difference between group 0.6% group and the pure group while there was a no significant decrease between the 0.3% and 0.6% group with the higher hardness mean in the 0.3% compared to 0.6% group. For the transverse strength, both 0.3% wt concentration and 0.6% concentration showed significant difference compared to the pure group and also between each other with the lowest impact strength in 0.6% group followed by 0.3% group with the highest transverse strength in the pure group. Conclusions: The silanation of halloysite nanotubes reduces the mechanical properties of the heat-cured acrylic denture base material. The more concentration of silanazed halloysite nanotubes is added, the more weakening occurs in the acrylic material relating to the hardness, transverse strength and impact strength.