The Frailty screening should be widely performed; however, simple and inexpensive biomarkers are missing. Biomarkers that can be routinely assessed in many patients are desirable. Recently, the hemoglobin-to-red cell distribution width ratio (Hb/RDW, HRR) has been suggested as a new prognostic marker and has been reported to be associated with inflammation, one of the factors contributing to frailty. Therefore, we aimed to address the role of HRR in frailty among 557 older outpatients (aged 65–96 years). Frailty was assessed using the Japanese version of the Cardiovascular Health Study criteria, and HRR was calculated from clinical records. Participants were classified into five groups based on a sex-stratified quintile of HRR (Q1–Q5). Of the participants, 20.3% were frail. Using multiple logistic regression models with the Q5 group as a reference, after adjusting for sex, age, body mass index, polypharmacy, pre-orthopedic surgery, and the use of iron medications, the multivariable-adjusted odds ratios (95% confidence intervals) of the Q4 to Q1 groups were 0.92 (0.58–1.47), 1.04 (0.67–1.61), 1.29 (0.84–1.96), and 1.85 (1.22–2.82), respectively, indicating that a lower HRR was significantly associated with frailty. The robustness of these results was also shown in the multiple imputation analysis. The results suggest that HRR measurement may be one of the indicators to identify frail older adults in routine practice.