Background: The pattern of fatigue in older psychiatric patients during the COVID-19 outbreak was unknown. This study examined the prevalence of fatigue and its association with overall quality of life (overall QOL) in clinically stable older patients with psychiatric disorders during the COVID-19 outbreak. Methods: This was a multicenter, cross-sectional study. Fatigue, depressive symptoms, pain, insomnia symptoms, and overall QOL were assessed with standardized instruments. Results: A total of 1063 patients were recruited. The prevalence of fatigue was 47.1% (95%CI: 44.1–50.1%). An analysis of covariance revealed that overall QOL was significantly lower in patients with fatigue compared to those without (P = 0.011). A multiple logistic regression analysis revealed that more severe depressive symptoms (OR = 1.15, P < 0.001), insomnia symptoms (OR = 1.08, P < 0.001) and pain (OR = 1.43, P < 0.001) were significantly associated with fatigue. Conclusions: Fatigue is common among clinically stable older patients with psychiatric disorders during the COVID-19 outbreak. Considering its negative impact on overall QOL, regular assessment of fatigue and appropriate treatment warrant attention in this subpopulation.