In this research study the effect of adding thermal cement as a filler on the properties of natural rubber STR20, through the preparation of natural rubber mixtures containing different ratios of thermal cement (0,5,10,15,20 pphr) on the rolling rubber machine, then characterization physico-mechanical properties and chemical of mixtures that prepared and then tested to measure the tensile strength, resistance friction and determine the hardness and swelling values in different solvents. The results showed increased tensile strength with increased thermal cement ratio until 15( pphr) but after this percentage take tensile strength to decline gradually, where the relationship becomes counterproductive between the additives and the resistance ratio, as noted the low percentage of elongation at break gradually with increasing the proportion of thermal cement, as for the hardness values it has increased in extrusive with increase the proportion of thermal cement in mixtures, also observed a decrease in friction resistance with increase the additives proportion even (15 pphr) to rise after that. Results of the study also showed that the samples swelling in mineral oil was lower compared to all of the gasoline and diesel, the swelling was in the mineral oil 1.29%, while in gasoline was 14.15% and in diesel was 12.43%.