Purpose: The purpose of this study was to develop a wellness index for workers (WIW) and examine the validity and reliability of theWIW for assessing workers’ wellness. Methods: The developmental process for the instrument included construction of a conceptualframework based on a wellness model, generation of initial items, verification of content validity, preliminary study, extraction of finalitems, and psychometric testing. Content validity was verified by 4 experts from occupational health nursing and wellness disciplines. The construct validity, convergent validity and discriminant validity were examined with confirmatory factor analysis. The reliabilitywas examined with Cronbach’s alpha. The participants were 494 workers from two workplaces. Results: Eighteen items were selectedfor the final scale, and the results of the confirmatory factor analysis supported a five-factor model of wellness with acceptablemodel fit, and factors named as physical · emotional · social · intellectual · occupational wellness. The convergent and discriminant validitywere also supported. The Cronbach’s alpha coefficient was .91. Conclusion: The results indicate that the WIW is a valid and reliableinstrument to comprehensively assess workers’ wellness, and to provide basic directions for developing workplace wellness program.