© 2021 by the authors. Licensee MDPI, Basel, Switzerland.This study aimed to evaluate the intra-and inter-rater reliability of a well-used and a less-used IsoMed-2000 dynamometer for knee flexion and extension peak torque (PT) measurements in a concentric test in athletes. Two IsoMed-2000 isokinetic dynamometers were used, an old one that was well-used and a new one that was less-used. Thirty-seven weight-lifting athletes (12 female, 25 male) were included in this study. Both legs of each athlete were tested twice on each isokinetic dynamometer at 60°/s and 180°/s. The Intraclass Correlation Coefficients (ICC), Standard Error Measurement (SEM), Smallest Detectable Change (SDC), SDC% and 95% limits of agreement were calculated to evaluate the intra-and inter-rater reliability of a well-used and a less-used IsoMed 2000 dynamometer for knee flexion and extension peak torque in athletes. Intra-rater reliability was moderate to excellent (ICCs: 0.516–0.928) for knee muscle strength parameters, and the highest SDC and SEM values were 0.76 N/kg and 0.28 N/kg, respectively. Inter-rater reliability was moderate to excellent (ICCs: 0.519–915) for knee muscle strength parameters, and the highest SDC and SEM values were 0.81 N/kg and 0.29 N/kg, respectively. At least 89.2% of the obtained values of parameters fell within the 95% limits of agreement. Our findings demonstrate the intra and inter-rater reliability of a Well-Used and a Less-Used IsoMed 2000 Dynamometer for Knee Flexion and Extension Peak Torque in Athletes.