The contact stress that occurs in the ultra-high molecular weight polyethylene (UHMWPE) hip joint cup has been shown to be correlated with the implant wear rate. The wear of the hip joint is considered as one of the main factors that affect the long term performance of the implant. The contact stress that occurs in the UHMWPE hip joint cup is affected by the implant dimensions and materials. In this study, four different femur materials and geometries were used to investigate the effects of femur design parameters on the resultant contact stress on the UHMWPE cup. The results of the finite element (FE) simulation show that the contact stresses at the UHMWPE cup decreases dramatically with increasing the femur diameter. Also the results indicated that the contact stresses on the UHMWPE cup decrease significantly when using functionally graded (FG) femur with low modulus of elasticity. The presence of metal backing results in a slight reduction in the UHMWPE cup contact stresses especially for small femurs. Finally, the presence of a gap between the UHMWPE cup and the femur results in a remarkable increase in the cup stress especially for a small femur. The hip joint femur dimensions and materials are thought to play an important role in the transition of load in the implant and should be taken into consideration during the design of the hip joint.