BACKGROUND: The rising prevalence of mild cognitive impairment (MCI) among older adults in nursing homes necessitates effective interventions to slow the progression to dementia. Integrated social-art interventions have shown promise in enhancing cognitive function and reducing social isolation. This study aimed to evaluate the effects of such an intervention on cognitive and psychosocial outcomes in older adults with MCI. METHODS: An explanatory sequential mixed-methods study was conducted, comprising a cluster randomized controlled trial (RCT) and a descriptive qualitative study. Four nursing homes in two districts of a city in southeastern China were randomly assigned (1:1) to either the intervention or the control group. The intervention group received a 14-week, 28-session integrated social-art program structured around theme-based group activities, while the control group received usual care, including assistance with daily living activities, basic medical care, recreational activities, and environmental cleaning. Quantitative outcomes were measured at baseline (T0), immediately post-intervention (T1), and at 24-week follow-up (T2), with global cognitive function as the primary outcome, and specific cognitive functions, psychosocial indicators, functional abilities, and quality of life as secondary outcomes. Qualitative interviews were conducted post-intervention to explore the reasons underlying the observed variations in efficacy. RESULTS: Eighty older adults with MCI (median age 86.50 years) participated, with an average attendance rate of 86.25% in the intervention group. Intention-to-treat analyses revealed a significant improvement in global cognitive function at T1 in the intervention group compared to the control group (β = 2.85; 95%CI [1.27, 4.44], P < 0.001); however, this effect was not sustained at T2. No significant improvements were observed in psychosocial indicators, functional abilities, or quality of life (P > 0.05). Qualitative findings indicated that structured, sequential tasks and professional guidance contributed to short-term cognitive gains, whereas age-related health issues and limited ongoing engagement impeded the durability of these benefits. CONCLUSIONS: The 14-week integrated social-art intervention appears feasible and may promote short-term cognitive activation in institutionalized older adults with MCI, though its benefits were not sustained at follow-up. Future research should investigate strategies for maintaining cognitive improvements and explore modifications to enhance broader clinical outcomes in this vulnerable population. TRIAL REGISTRATION: The trial was prospectively registered at the Chinese Clinical Trials Registry with the registration number ChiCTR2200061681 on 30 June 2022.