Objective: To assess content validity, construct validity, and reliability of Relational Ethics Scale (RES) in Thai version.
Materials and Methods: The researcher translated RES into Thai and then translated back into English. Then, RES in Thai version was given to 120 patients aged between 18 to 60 years in Department of Psychiatry, HRH Princess Maha Chakri Sirindhorn Medical Center. Content validity was measured by item-objective congruence index (IOC). Construct validity was measured by confirmatory factor analysis (CFA), referred from the Root Mean Square Error of Approximation (RMSEA) and loading factor. Cronbach’s alpha coefficient was used for reliability measurement.
Results: IOC of RES in Thai version was 0.86, RMSEA was 0.06, the loading factor of all questions >0.30, and overall internal consistency of RES was 0.96.
Conclusion: RES in Thai version contained content validity and construct validity. If it is developed further to determine predictive, concurrent validity and determine sensitivity and specificity, it can be used for evaluation and treatment planning accurately in psychological intervention.

Keywords: Relational ethics scale; Thai version; Vertical relationship; Horizontal relationship