The connecting rod, as an important part in internal combustion engines, has been most widely used in automotive industry, and its main function is to transfer the reciprocating motion of the piston into the rotatory motion of the crankshaft. In this study, fatigue analysis of the connecting rod is performed numerically for different engine speeds. With this aim, it is attempted to reduce the weight of the connecting rod by choosing the low density and high strength of GFRP and CFRP composite materials instead of structural steel. In this way, it is possible to improve the engine efficiency with saving unnecessary balancing weights as well as reducing the cost of the connecting rod. In the current study, the connecting rod was modeled using Solidworks software, and its CAD model was transferred to the ANSYS/Workbench software for Finite Element Analyses (FEA). In FEA, fatigue analyses were performed to determine fatigue parameters such as alternating stress, deformation, fatigue life and safety factor according to Soderberg’s fatigue model. Results from this study showed that alternating stress and safety factor reached a critical value between piston pin end and crank end near to the piston pin end. Alternating stress values of the GFRP and CFRP connecting rods were much lower than those of structural steel rod. In contrast to reduction of the weight by 1/5, fatigue life of the connecting rod with structural steel material was much greater than those of GFRP and CFRP providing a higher safety factor compared with composite materials.