Context: Knee joint-position sense (JPS) is a key parameter for optimum performance in many sports but is frequently negatively affected by injuries and/or fatigue during training sessions. Although evaluation of JPS may provide key information to reduce the risk of injury, it often requires expensive and/or complex tools that make monitoring proprioceptive deterioration difficult. Objective: To analyze the validity and reliability of a digital inclinometer to measure knee JPS in a closed kinetic chain (CKC). Design: The validity and intertester and intratester reliability of a digital inclinometer for measuring knee JPS were assessed. Setting: Biomechanics laboratory. Participants: 10 athletes (5 men and 5 women; 26.2 ± 1.3 y, 71.7 ± 12.4 kg; 1.75 ± 0.09 m; 23.5 ± 3.9 kg/m2). Intervention: Knee JPS was measured in a CKC. Main Outcome Measures: Absolute angular error (AAE) of knee JPS in a CKC. Results: Intraclass correlation coefficient (ICC) and standard error of the mean (SEM) were calculated to determine the validity and reliability of the inclinometer. Data showed that the inclinometer had a high level of validity compared with an isokinetic dynamometer (ICC = 1.0, SEM = 1.39, P < .001), and there was very good intra- and intertester reliability for reading the inclinometer (ICC = 1.0, SEM = 0.85, P < .001). Compared with AutoCAD video analysis, inclinometer validity was very high (ICC = 0.980, SEM = 3.46, P < .001) for measuring AAE during knee JPS in a CKC. In addition, the intertester reliability of the inclinometer for obtaining AAE was very high (ICC = .994, SEM = 1.67, P < .001). Conclusion: The inclinometer provides a valid and reliable method for assessing knee JPS in a CKC. Health and sports professionals could take advantage of this tool to monitor proprioceptive deterioration in athletes.