Purpose: Silicone-based elastomeric materials are commonly used to fabricate maxillofacial prostheses. The aim of this study was to evaluate the effect of different types of silica and nanosized titanium dioxide addition on the mechanical properties of two RTV silicone elastomers. Materials and Methods: A-2000 and A-2006 silicone elastomers were used, and each was divided into four subgroups (n = 5). The first group was the control without additives. Other groups were titanium dioxide, fumed silica, and silaned silica. Each specimen was prepared in compliance with the manufacturer's instructions for the tensile strength, percent elongation, tear resistance, and the hardness tests according to ISO and ASTM standards. A factorial ANOVA with pairwise interaction indicated that the pattern for all four outcomes of the materials was different for A-2000 and A-2006 (p < 0.05). Therefore, the average outcome values for the materials within silicone elastomers were then analyzed by Tukey HSD. For the hardness test results, Kruskal-Wallis and Mann-Whitney U test methods were used. The level of statistical significance was p < 0.05. Results: There was a statistically significant interaction (p < 0.05) between materials and silicone type for all four tests (tensile strength, tear, hardness, percent elongation). The hydrophobic silica group had significantly higher tensile strength than TiO2 for A-2000. The fumed hydrophilic silica group had significantly higher tensile strength than TiO2 for A-2006. Most of silica specimens had higher tensile strength when compared with the control and TiO2 groups for A-2000 and A-2006 silicones. The TiO2 group had the highest hardness value for A-2000 while the lowest hardness value for A-2006 (p < 0.05). There was no significant difference of tear strength among the type of additives (p > 0.05) for A-2000. The fumed silica and TiO2 groups had significantly higher tear strength than the control group for A-2006. The fumed silica and the hydrophobic silica groups had significantly higher percent elongation than the control group (p < 0.05) for A-2000. The TiO2 group had the lowest percent elongation for A-2006. Conclusions: Results in this in vitro study may clarify future studies about the effect of different additives on the physical and mechanical properties of maxillofacial elastomers. There is a great interest in the effect of a new-generation hydrophobic silica incorporation into A-2000 silicone as well as the effect of fumed hydrophilic silica incorporation into A-2006 silicone. Future research should be supported with more in vitro trials in different percentages of such additives used in this study.