This study was conducted to determine whether the mechanical fatigue and chemical aging protocols could be utilized interchangeably when flexural strength and surface microhardness of dental resin composites are to be evaluated. In other words, do their effects on testing parameters; flexure strength and microhardness; are comparable to induce the same effect or not? Two types of resin composite material models; nanohybrid (FiltekTm Z250 XT) and nanofilled (FiltekTm Z350 XT) were used in this study. Method: Sixty specimens were prepared from each composite type. Rectangular specimens (n= 30) and disc shaped specimens (n=30) were divided into four groups as followed; (Gp 1A) Control group of nano hybrid composite specimens, (Gp 2A) mechanically aged nano hybrid composite specimens, and (Gp 3A) chemically aged nano hybrid composite specimens. Nano filled composite specimens were designated as Gp 1B, Gp 2B and Gp 3B for the same aging treatments respectively. Each group contained 20 specimens; 10 rectangular and 10 disc shaped. For mechanical fatigue, the specimens were subjected to 6000 cyclic loading at 23.5 N, while chemical aging was done by storing the specimens in acidic artificial saliva at pH of 3.6 for 8 days. The rectangular specimens were used for 3-point flexure strength evaluation using a universal testing machine at a crosshead speed of 0.5 mm/minutes. The disc shaped specimens were used for surface microhardness testing. The surface microhardness was measured by using Digital Display Vickers Micro-hardness Tester. Results: Both aging protocols induced significant reduction in the two testing properties; the flexure strength and the microhardness. Regarding flexure strength, Gps 2A & 2B did not differ significantly from each other, but were significantly weaker than Gps 1A & 1B. In addition, Gps 3A & 3B did not differ significantly from each other, but were significantly weaker than all former groups. The highest decline in flexure strength was recorded with Gp 2B. Microhardness testing revealed insignificant difference among Gps 1A, 1B and 2A. Groups 2B & 3B were significantly softer than the previous groups, but they did not differ significantly from each other. The last group, Gp 3A was significantly softer than all other groups. Conclusions: With the limitations of this study, it might be accepted to use chemical aging protocol interchangeably with mechanical fatigue aging protocol, only if we consider flexure strength parameter. For surface microhardness assessment, mechanical fatigue aging protocols cannot be used interchangeably.