This study aimed to develop and determine the test-retest, intra- and interrater reliability, and validity of the Closed Kinetic Chain Lower Extremity Stability Test (CKCLEST). Three-blinded, cross-sectional, repeated-measures clinical measurement reliability trial. Fifty young adults participated in this study. To assess the reliability of CKCLEST, intraclass correlation coefficient, standard error of measurement, minimal detectable change, and Bland–Altman plot were used. For concurrent validity of CKCLEST was applied Spearman correlation analysis with Vertical Jump Test, Isokinetic Dynamometer Test, Single-Leg Hop Test, and Prone Bridge Test. All analyses were made for both the best score and the average score. CKCLEST showed excellent reliability. ICC for test-retest reliability (0.93; 0.84), intrarater reliability (rater 1: 0.90; 0.83- rater 2: 0.93; 0.85), and interrater reliability (0.90; 0.83) was calculated for average score and best score, respectively. CKCLEST was found to be moderately correlated with each of the tests. CKCLEST is a highly reliable, valid, and new clinical assessment tool.