Fatigue behaviour of rubber is a very important characteristic due to its extensive use in many engineering applications. In most applications, rubber is commonly subjected to fluctuating loads, which often lead to failure due to the nucleation and growth of defects or cracks. Due to their viscoelastic behavior, rubbers have a high damping ability. Very often rubbers are subjected to different frequencies in the service, such as engine mounts. The effect of frequency on the fatigue lifetime needs deep investigations. In present work, the effect of frequency on the styrene butadiene (SBR) and nitrile-butadiene rubber (NBR) with 0,20,30,50 and 70 Phr of carbon black was investigated. It was found that the fatigue lifetime decreased with the increase of the frequency. Increasing carbon black (CB) contents in rubber improved the fatigue resistant and increased of the fatigue lifetime.