Blends of Natural Rubber/Styrene Butadiene Rubber (NR/SBR) loaded with different ratios of N220:N774 carbon black fillers were prepared. The mechanical properties of pure blends and those loaded with different ratios of carbon black were investigated. The (50NR/50SBR), 40N220/(50NR/50SBR) and 60N774/(50NR/50SBR) blends were found to exhibit the highest values of tensile strength and elongation at break. The theoretical Mooney-Rivlin model applied to NR/SBR and supports the result of stress-strain. (50NR/50SBR) blends loaded with mixed ratios of N220 and N774 were also prepared. The stress-strain study of them did not show any significant change due to the order of addition of carbon black. The values of shore hardness (A) for all samples were measured and showed a marked increase by increasing the black content.