OBJECTIVE: The aim of the study is to explore the potential of a sitting reduction workplace intervention for improving stress and work performance. METHODS: A cluster randomized controlled trial evaluated an intervention to reduce and break up occupational sitting in 12 clusters ( n = 89 office workers) over 8 weeks. Outcomes were physiological stress (cortisol concentrations), perceived stress, and work performance. RESULTS: Linear mixed model group × time interaction effects were nonsignificant. Exploratory analyses showed a trend, with a large effect, for lower cortisol concentrations over the day in the intervention group relative to controls at 8 weeks (-0.85; 95% confidence interval, -1.70 to 0.03 nmol·L -1 ; P = 0.06, d = 0.79). The intervention group had higher vigor and cognitive liveliness at 8 weeks relative to controls ( P ≤ 0.05). CONCLUSIONS: This exploratory study suggests that there could be meaningful changes in physiological stress and work-related outcomes that should be investigated in future studies.