Objective: There are many cases of potentially impaired cognitive function in older patients with hypertension. Therefore, we investigated factors associated with one-year changes in cognitive function in older hypertensive patients during outpatient visits. Design and method: We included 223 hypertensive patients (age 76.3 ± 6.3 years, 106 males) aged 65 years or older who attended outpatient hypertension clinics at six specialized institutions nationwide and had no prior diagnosis of dementia. We obtained the mini-mental state examination (MMSE) from all participants. We defined the impaired cognitive function as an MMSE score of 27 or less. At baseline and one year later, the participants were evaluated for comprehensive geriatric assessment, including MMSE, and muscle strength, with the converted group defined as having new cognitive decline at one year and the reverted group as having cognitive improvement one year after the cognitive decline. All participants gave informed consent, and our institutional review board approved the study protocol. Results: At baseline, 81 of 223 elderly hypertensive patients had impaired cognitive function. At one-year follow-up, 40 of 142 patients in the maintained cognitive function group were classified as converted, and 33 of 81 patients in the impaired cognitive function group were classified as converted. The converted group was older than the cognitively intact group (76.8 vs. 73.9 years, p < 0.05), had higher home blood pressure, and had more significant grip strength loss over the year. Multivariate analysis identified age (odds ratio 1.1, 95% CI 1.0–1.2) and change in grip strength (odds ratio 0.84, 95% CI 0.72–0.99) as factors associated with the converted group. The reverted group was younger, had a higher percentage of males, and had weaker grip strength than the group with persistent cognitive decline. In multivariate analysis, grip strength (odds ratio 0.80, 95%CI 0.68–0.94) was extracted as a factor associated with the revert group. Conclusions: Potential cognitive decline was observed in 36% of older patients with hypertension. Furthermore, we examined a high rate of cases of cognitive function change over one year. Age and grip strength decline was considered responsible for cognitive conversion and baseline grip strength for revert, respectively.