Functional tests are often used to assess knee function after knee ligament injuries. However, the reliability and validity of these tests have not been sufficiently studied. The main purpose of this study was to examine six functional knee tests in order to establish the tests according to functional demands. The functional tests (vertical jump, figure-of-eight, stairs-running, triple jump, stairs hopple, and side jump tests) were evaluated on 35 patients after anterior cruciate ligament reconstruction (mean = 18 months postoperative). Evaluative variables were the Lysholm functional score, thigh atrophy, and knee instability. Factor analysis was used to identify knee tests based on the same basic variables in order to employ the most representative tests. The factor analysis disclosed two factors that reflected diverse functions. The first factor had significant correlation to the Lysholm score (daily life function) and was best represented by the figure-of-eight and stairs-running tests. The second factor was best correlated to the strength/stability function and was best represented by the triple jump test and the new stairs hopple test. Thus, the tests were categorized according to functional demands--daily life function and strength/stability function. The Lysholm functional score was inaccurate in identifying functional problems during strenuous activities.