In the present study, the Flexural strength of nanohybrid composite was compared with conventional microfilled composite resin in vitro. Thirty nanohyrid and 30 conventional microfilled composite resins were subjected to Flexural strength measurement as follows; a teflon mold (4 mm in diameter and 6 mm in depth) was filled with materials, light cured through the glass slides for 40 sec top and bottom surfaces. Then the specimens were taken out from the mold, again light curing for 40 sec, stored in dry condition and placed into a Flexural strength tester and loaded until fracture of the sample. Student t-test was performed to assess the differences between two groups and a value of p >0.05 was considered as statistically significance. The results showed that the means ± SD Flexural strength of nanobybrid and conventional microfilled composite resin were 118.70 ± 3.90 Mpa and 77.43 ± 2.65 Mpa, respectively and the differences were statistically significant. It can be concluded that nanohybrid is superior to conventional microfilled composite resin in respect to Flexural strenth in class II restorations of permanent molar teeth.