In applied organizational research, where economy of scale is often a crucial factor in successful assessment, ultra-short measures are often needed. This study investigates the psychometric properties of the Reduced Affective Well-Being Scale (RAWS), an ultra-short measure of positive and negative affect in the workplace. This 6-item ultra-short version was compared with the original 12-item scale proposed by Segura and González-Romá (2003) in terms of internal consistency and criterion validity, using a sample of 1117 bank employees. In addition, longitudinal measurement invariance and within-subject reliability of the RAWS over time were assessed in a longitudinal sample of 458 employees at 12 time points. Results provide evidence that the RAWS is similar to the full scale in terms of reliability and validity. In addition, the RAWS shows satisfactory within-person reliability and factor loading invariance over time. In studies with intensive longitudinal designs that require repeated measures of affective well-being, the use of RAWS is a recommendable option.