Biomechanics is the application of mechanical principles on living organisms for the purpose of understanding better the influence of mechanical loads on the structure, properties, and function of living things. In recently, experimental techniques in biomechanics have undergone enormous developments. Having a clearer understanding of the organ’s mechanical conditions make further enhancements in prosthetic devices, and improvements may be made for surgery and implant designs to help patients operations. Compared to the other limb, bones have most portion in musculoskeletal injuries. One of the most important bone in human body is femur. In human anatomy, femur is the longest and largest bone in the body that forms part of the hip joint at the proximal. The entire weight of the upper body, from the hip onwards, is transmitted to the legs through the two femurs. The femur performs various functions that help to maintain mobility of the body. An incident diseases in children that affects the head of the femur is “Perthes”. In Perthes disease, the blood supply to the rounded head of the femur is temporarily disrupted. Without an adequate blood supply, the bone cells die and as a result the bone softens and breaks down. The goal of treatment this disease is to relieve painful symptoms, protect the shape of the femoral head, and restore normal hip movement. There are many treatment options for Perthes disease such as observation, bed rest and crutches, a plaster cast or special leg brace, or surgery. All of these treatments can be improved by knowing the clear details of mechanical properties of femur such as stress distribution within femur and forces that are applied to the femur. The aim of this study is extraction stress distribution and forces acting on the femur of the person with Perthes disease. The head of right femur has been deformed and exited from hip socket due to Perthes, caused person limping while walking. To reach this goal, CT scans of a patient will first be processed, and a 3D model of the hip region created in Mimics software. The model was then exported to a pre-processing software called Hypermesh in order to generate volumetric mesh. Then, the ten mechanical properties assigned to meshed model of femur according to bone density and gray values of each part. Then, the forces that are applied to the head of femur during walking is determined by simulating the movement of persons in Opensim software. After that, a finite element analysis be carried on femur model to evaluate the stress distribution in Perthes and health (right and left) femur. A maximum reaction force acting on the head of the femur was applied on the region that has been created from contact of pelvis and femur while fixed support is provided at the end of femur. Finally, the effect of femur rotation during the movement of the person and effect of cartilage on stress distribution within femur was evaluated. The results show that stress concentration occurred in head of Perthes femur and greater force and stress applied on this femur rather than health femur. Also, rotation of femur and placed it in original state at the time of maximum force caused the amount of stress and shear stress increased in femur. Due to femur is weaker in shear stress rather than normal stress, rotation of femur particular femur’s flexion, is the more critical state in femur. The inclusion of cartilage caused a significant decrease in magnitude of stresses and more uniform stress distribution within the femur. Keywords: Femur, Perthes, Soft Tissue, Finite Element Analysis of Femur