AbstractArthritis is a major cause of functional decline, which affects the quality of life (QoL) of older adults. This study analyzed instrumental activities of daily living (IADL) patterns in older adults with arthritis and the risk factors of functional decline. Data from the Korean Longitudinal Study of Aging (KLoSA), in which the participants were community-dwelling older adults aged ≥ 65 years and conducted every two years, were used to examine patterns in IADL performance between 2006 and 2016. The participants comprised 1,822 older adults, divided into an arthritis group and a non-arthritis group. A Generalized Estimating Equations (GEE) model and Kaplan–Meier analysis was used for the data analysis. The arthritis groups showed a statistically significant decrease in IADL function in 2012 (β = 1.283, p = 0.026), 2014 (β = 1.323, p = 0.028), and 2016 (β = 1.484, p = 0.014). The GEE model identified psychological conditions (depressive symptoms, cognitive function) and number of chronic diseases in the arthritis group as risk factors for increased IADL dependence. Healthcare providers should develop strategies to manage long-term functional decline, including programs to manage and prevent chronic diseases, cognitive function decline, and keep depressive symptoms under control, beginning within six years of arthritis diagnosis.