Objective to investigate the anatomical relationship between the posterior sagittal septum of knee and the tibial insertion of posterior cruciate ligament (PCL). Methods Twentytwo fresh frozen adult cadaveric knee joints were dissected. With the knee flexed to 90 degrees, PCL was divided into anterolateral bundle and posteromedial bundle. The outlines of the footprints of the two bundles were marked with ink. The posterior sagittal septum of knee and the insertion of PCL on tibia were observed and measured. Results There was a sagittal septum in the knee, the anterior of which was connected with fat pad, alar fold or mucous ligament. The middle part of the sagittal septum lied between the anterior and posterior cruciate ligament, the postetior part of the sagittal septum formed the posterior septum of the knee. Eight of the 22 knees (36.36%), the posterior sagittal septum passed the PCL at lateral side. And 14 of the 22 knees (63.64%), the sagittal septum passed around the bundle of PCL. Moreover, the center of the tibial insertion of anterolateral bundle of PCL located at （0.90±2.40）mm medially to the posterior sagittal septum ,and at （3.25±1.20）mm beneath the lateral tibial surface. The posteromedial bundle was seated at （4.35±2.46）mm medially to the posterior sagittal septum and at （6.91±1.57）mm beneath the lateral tibial surface. Conclusion The anatomical relationship between the posterior sa