The effect of different grades (N375, N405, N509) of carbon black (CB) powder on the synthesised carbon black natural rubber (CBNR) composites were investigated to study the curing and reinforcing characteristics of CB structure. The different CB grades depicted; on the one hand, the ascending order of nitrogen surface area (NSA) in conjunction with statistical thickness surface area (STSA) to be N375 < N405 < N509, while on the other hand, relative span factor (RSF) together with pellet hardness were N405 < N509 < N375. The synthesised CBNR composites were analysed for rheological and reinforcement behaviour. It was observed that both, elongation at break and cure rate index (CRI) of the CBNR composites varied with RSF of CB powders. The RSF of CB powders showed association with elongation at break and CRI of the CBNR composites. Moreover, there is a synergy in the hardness, resilience and tensile strength of the CBNR composites.