Background <p>Chronic pain is associated with frailty in older adults; however, the mechanisms underlying this relationship are not fully understood.</p> Aims <p>To examine whether sleep quality is involved in the longitudinal association between chronic pain and frailty progression in community-dwelling older adults.</p> Methods <p>This longitudinal study included 363 community-dwelling adults aged ≥ 65 years who participated in the 2018 and 2019 waves of the Tarumizu Study in Japan. Chronic pain was defined as self-reported lower back and/or knee pain lasting for at least 2 months. Sleep quality was assessed using a single-item questionnaire and categorized as good, medium, or poor. Frailty was assessed using the Kihon Checklist, and progression was defined as an increase ≥ 2 points over 1 year. Logistic regression and mediation analyses were conducted.</p> Results <p>Frailty progression was observed in 27.3% of participants. Chronic pain was significantly associated with frailty progression (odds ratio [OR]: 1.79; 95% confidence interval [CI]: 1.08–2.97), although this association was attenuated after adjustment for sleep quality. Poor sleep quality was independently associated with frailty progression (OR: 2.02; 95% CI: 1.04–3.91). Mediation analysis showed a significant indirect effect of chronic pain on frailty progression through sleep quality (β = 0.08; 95% CI: 0.001–0.20).</p> Discussion <p>Poor sleep quality may represent one potential pathway underlying the association between chronic pain and frailty progression in community-dwelling older adults.</p> Conclusions <p>Integrated assessment of pain and sleep problems may help identify older adults at greater risk of frailty progression.</p>