Pain is a key symptom of osteoarthritis (OA) and has been linked to poor mental health. Pain fluctuates over time within individuals, but a paucity of studies have considered day-to-day fluctuations of joint pain in relation to affective symptoms in older persons with OA. This study investigated the relationship of pain severity as well as within-person pain variability with anxiety and depression symptoms in 832 older adults with OA who participated in the European Project on OSteoArthritis (EPOSA): a 6-country cohort study. Affective symptoms were examined with the Hospital Anxiety and Depression Scale, pain severity was assessed with the Western Ontario and McMaster Universities OA Index and the Australian/Canadian Hand Osteoarthritis Index, and intraindividual pain variability was measured using pain calendars assessed at baseline, 6, and 12 to 18 months. Age-stratified multiple linear regression analyses adjusted for relevant confounders showed that more pain was associated with more affective symptoms in older-old participants (74.1–85 years). Moreover, older-old participants experienced fewer symptoms of anxiety (ratio =.85, 95% confidence interval [CI],.77–.94), depression (ratio =.90, 95% CI,.82–.98), and total affective symptoms (ratio =.87, 95% CI,.79–.94) if their pain fluctuated more. No such association was evident in younger-old participants (65–74.0 years). These findings imply that stable pain levels are more detrimental to mental health than fluctuating pain levels in older persons. Perspective: This study showed that more severe and stable joint pain levels were associated with anxiety and depressive symptoms in older persons with OA. These findings emphasize the importance of measuring pain in OA at multiple time points, because joint pain fluctuations may be an indicator for the presence of affective symptoms.