Context: New methods are being validated to easily evaluate the knee joint position sense (JPS) due to its role in the sports movement and the risk of injury. However, no studies to date have considered the open kinetic chain (OKC) technique, despite the biomechanical differences compared with closed kinetic chain movements. Objective: To analyze the validity and reliability of a digital inclinometer to measure the knee JPS in the OKC movement. Design: The validity and intertester and intratester reliability of a digital inclinometer for measuring knee JPS were evaluated. Setting: Sports research laboratory. Participants: A total of 18 athletes (11 males and 7 females; 28.4 [6.6] y; 71.9 [14.0] kg; 1.77 [0.09] m; 22.8 [3.2] kg/m2) voluntary participated in this study. Main Outcomes Measures: Absolute angular error (AAE), relative angular error (RAE), and variable angular error (VAE) of knee JPS in an OKC. 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 excellent validity of the inclinometer to obtain proprioceptive errors compared with the video analysis in JPS tasks (AAE: ICC = .981, SEM = 0.08; RAE: ICC = .974, SEM = 0.12; VAE: ICC = .973, SEM = 0.07). Intertester reliability was also excellent for all the proprioceptive errors (AAE: ICC = .967, SEM = 0.04; RAE: ICC = .974, SEM = 0.03; VAE: ICC = .939, SEM = 0.08). Similar results were obtained for intratester reliability (AAE: ICC = .861, SEM = 0.1; RAE: ICC = .894, SEM = 0.1; VAE: ICC = .700, SEM = 0.2). Conclusions: The digital inclinometer is a valid and reliable method to assess the knee JPS in OKC. Sport professionals may evaluate the knee JPS to monitor its deterioration during training or improvements throughout the rehabilitation process.