Frailty is considered a multidimensional geriatric syndrome, manifested by the accumulation of age-associated deficits. The consequences of frailty transitions are still understudied. This study evaluated the influence of frailty transitions on cognitive function in the older adult population. We used data derived from the Korean Longitudinal Study of Aging (KLoSA) (2008-2018) on older adults aged ≥ 65 years. Frailty was assessed using a validated Korean frailty measure known as the frailty instrument (FI), and cognitive function was measured using the Korean version of the Mini-Mental State Examination (K-MMSE). Transitions in frailty and their relationship with cognitive function were investigated using lagged generalized estimating equations (GEE), t-tests, and ANOVA. Respondents who experienced frailty transitions (those with ameliorating frailty), those who developed frailty, and whose frailty remained constant, were more likely to have a lower cognitive function than those who were consistently non-frail. Older age, activities of daily living (ADL) disability, and instrumental ADL disability were more negatively associated with declining cognitive function, especially in the "frail → frail" group. Changes in all individual components of the frailty instrument were significantly associated with impaired cognitive function. The results suggest an association between frailty transitions and cognitive impairment. Over a 2-year span, the remaining frail individuals had the highest rate of cognitive decline in men, while the change from non-frail to frail state in women was significantly associated with the lowest cognitive function values. We recommend early interventions and prevention strategies in older adults to help ameliorate or slow down both frailty and cognitive function decline.