Purpose: This study evaluated the effect of resin thickness from both {Sonic Fill resin composite (SF)& Tetric N Ceram Bulk Fill resin composite (TNB)} on polymerization shrinkage strains, depth of cure and degree of conversion. Material and Methods: A total of 70 specimens were prepared and Polymerization shrinkage strains were measured by strain gauge foil connected to the computer software program which gave the results. Depth of cure (DOC) was measured by Vickers microhardness tester applying a 50g load through a Vickers indenter with a dwell time of 10s and expressed as mean of hardness ratio. Degree of conversion (DC%) was measured using Fourier transform infrared spectroscopy by potassium bromide pellet technique. All recorded data were presented, tabulated and statistically analyzed. Results: the strains resulted from both materials increased with increasing the thickness of the specimens from 2mm to 4mm but decreased at 6mm. There was a statistically significant increase in depth of cure and degree of conversion in SF than in TNB at all specimen thickness. Conclusions: Bulk fill resin composite in thickness more than 4mm affect the physical properties; degree of conversion, depth of cure and polymerization shrinkage.