An artificial knee joint comprises a femoral component a tibial plate slidably receive the femoral component. The femoral component includes medial and lateral condyles, an opening and an elliptical spherical sliding portion are formed therebetween. The elliptical spherical sliding portion couples posterior ends of the medial and lateral condyles, and slides with respect to the tibial plate when flexing the knee joint. The tibial plate includes a medial fossa and a lateral fossa, and a spine and a concave sliding surface are formed therebetween. The spine moves within the opening in an antero-posterior direction in response to flexion-extension action of the knee joint, and comes into contact with the sliding portion when flexing. The concave sliding surface forms a posterior surface of the spine, and slidably receives the elliptical spherical portion. A width of the elliptical spherical sliding portion is widened from the opening toward a posterior end.
