The amalgams traditionally used in dental fillings cause a number of serious health problems, largely due to the mercury they contain. Furthermore, amalgam fillings, which do not match the colour of the tooth, also have a negative effect on aesthetics. On the other hand, the development of resin-based dental composites, which have a good aesthetic appearance due to their compatibility with tooth colour, high mechanical properties, high radiopacity, low polymerisation shrinkage and ease of application, have become the preferred alternative to amalgam fillings in dentistry. In this thesis, the effects of different concentrations (wt.%) of zirconia and barium glass nanoparticles on the mechanical and physical properties of the resin based composite were studied. The total filler concentration of the composites was 65 wt.%. The composites were prepared by dispersing 20 wt.% and 30 wt.% surface modified barium glass, 1 wt.% and 2 wt.% surface modified zirconia nanoparticles in the monomer mixture containing 40 wt.%, 30 wt.% and 30 wt.% Bis-GMA, UDMA and TEGDMA, respectively. The mechanical properties; flexural strength and compressive strength, depth of cure, polymerization shrinkage and water sorption and solubility of the resin based composites were examined. The fracture surface of composites was investigated using scanning electron microscopy (SEM). Three point bending and compression test results showed that barium glass and zirconia nanoparticles noticeably enhanced the mechanical properties of the composites. The Ba30Z1 sample containing 30 wt.% barium glass and 1 wt.% zirconia achieved the highest flexural strength of 79.09 ± 3.32 MPa with a 37% increase over the reference sample. The Ba20Z2 sample containing 20 wt.% barium glass and 2 wt.% zirconia achieved the highest compressive strength of 250.05 ± 8.01 MPa with a 41% increase over the reference sample.