股骨（Os femoris或者简为Femur）是人体最长最粗壮的长骨。股骨位于四肢动物的下肢（或后肢）深面。

股骨上方弯曲，在此有股骨头（Caput femoris），近圆形，其关节面与骨盆形成髋关节。弯曲的部分被称作股骨颈（Collum femoris）。这种弯曲连接能有效降低外界对骨盆的冲击，股骨颈有如一缓冲器。

相对股骨头有一骨性突起，被称为大转子（Trochanter major）。它是臀大肌，臀中肌和臀小肌的附着点。在内侧有小转子（Trochanter minor），它是髂肌和腰大肌的附着点。一些哺乳类动物，（如马，兔）还有第三转子（Trochanter tertius）。

The femur (/ˈfiːmər/, pl. femurs or femora /ˈfɛmərə, ˈfɛmrə/) or thighbone, is the most proximal (closest to the center of the body) bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in the hindlimbs. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia and kneecap forming the knee joint. By most measures the femur is the strongest bone in the body. The femur is also the longest bone in the body.