The aim of this study was to examine the reliability and validity of the Professional Suitability Scale (PSS) for social work. A test–re-test design was used to collect data from social work undergraduate students in Hong Kong (n = 269). The instrument administered was a self-report questionnaire survey. Results of this study showed that the PSS established modest-strong stability reliability (r = 0.62) and moderate concurrent validity. For construct validity testing, the final 18-item second-order three-factor model of the PSS met nine out of ten model fit indices in the confirmatory factor analysis. The internal consistency on this final 18-item PSS was excellent (α = 0.90). This study, which corroborated the findings of previous studies on excellent internal consistency, has filled the research gap on stability reliability and has affirmed construct validity. Significant implication of this study is the potential use of the PSS for assessing professional suitability with social work students throughout the educational programmes.