Eighty-two patients with coexisting knee osteoarthritis (KOA) and type 2 diabetes mellitus (T2DM) were randomized to outdoor green cycling (n=41) or indoor stationary cycling (n=41). The primary outcome of interest was HbA1c. Secondary outcomes of interest included KOOS subscales, perceived stress (PSS), mood (POMS and subscales), self-esteem (RSE), BMI, enjoyment, and intention to continue exercising. Outcomes were assessed at 6 and 24 weeks. Overall, the results of the study revealed larger HbA1c reductions, greater decreases in perceived stress and total mood disturbance, and superior gains in KOOS ADL/Sport/QoL and vigor with outdoor green exercise, alongside stronger intention to keep exercising. These findings suggest prescribing green-environment exercise for KOA and T2DM may confer incremental psychological and metabolic benefits beyond comparable indoor cycling.