This study examined the validity and reliability of the Assessment of Work Performance (AWP) using Rasch analysis. The AWP was administered to 365 clients with a variety of work-related problems. Rasch analysis and principal component analysis were used to examine the appropriateness of the rating scales and unidimensionality of AWP items. The person-response validity, internal consistency, targeting appropriateness, and differential item function were also analyzed. The Rasch analysis confirmed the 4-point rating scale, and the item set met the criteria of unidimensionality. The AWP exhibited satisfactory person-response validity and internal consistency. Among the three subdomains, the targeting of item-difficulty was sufficient in the motor skills and process skills subdomains. Differential item functioning was found across gender and diagnoses. This study presented evidence to support that the AWP functioned as a reliable and valid assessment in assessing work performance.