This article assesses the validity and reliability of the work ability index (WAI) for 1,436 nurses in three public hospitals in Rio de Janeiro, Brazil. The study estimated the dimensional validity by means of exploratory factor analysis, as well as correlational validity, relating WAI to theoretically relevant constructs. Reliability was evaluated by internal consistency analysis, using Cronbach's alpha and McDonald's omega. Factor analysis indicated a two-dimensional structure explaining 52.8% of the accumulated variance for the principal components and 42% for the principal axes. The theoretical hypotheses for the construct's validity were confirmed, with direct and significant correlation between the WAI and the reward, control, and self-rated health scores; an inverse and significant correlation with the scale on need for recovery after work, minor psychological disorders, effort, over-commitment, and demand. In conclusion, the WAI showed adequate psychometric properties.