Antihypertensive therapy is pivotal for reducing cardiovascular events. The 2019 Guidelines for the Management of Hypertension set a target blood pressure (BP) of <140/90 mmHg for persons older than 75 years of age. Optimal BP levels for older persons with frailty, however, are controversial because evidence for the relationship between BP level and prognosis by frailty status is limited. Here, we evaluated the relationship between systolic BP and frailty status with all-cause mortality in ambulatory older hypertensive patients using data from the Nambu Cohort study. A total of 535 patients (age 78 [70-84] years, 51% men, 37% with frailty) were prospectively followed for a mean duration of 41 (34-43) months. During the follow-up period, 49 patients died. Mortality rates stratified by systolic BP and frailty status were lowest in patients with systolic BP < 140 mmHg and non-frailty, followed by those with systolic BP ≥ 140 mmHg and non-frailty. Patients with frailty had the highest mortality regardless of the BP level. The adjusted hazard ratios (95% confidence intervals) of each category for all-cause mortality were as follows: ≥140 mmHg/Non-frailty 3.19 (1.12-11.40), <140 mmHg/Frailty 4.72 (1.67-16.90), and ≥140 mmHg/Frailty 3.56 (1.16-13.40) compared with <140 mmHg/Non-frailty as a reference. These results indicated that frail patients have a poor prognosis regardless of their BP levels. Non-frail patients, however, with systolic BP levels <140 mmHg had a better prognosis. Frailty may be a marker to differentiate patients who are likely to gain benefit from antihypertensive medication among older hypertensives.