Abstract Background Very few studies have examined the relationship of oral health with physical functioning and frailty in the oldest old (> 85 years). We examined the association of poor oral health with markers of disability, physical function and frailty in studies of oldest old in England and Japan. Methods The Newcastle 85+ Study in England (n = 853) and the Tokyo Oldest Old Survey on Total Health (TOOTH; n = 542) comprise random samples of people aged > 85 years. Oral health markers included tooth loss, dryness of mouth, difficulty swallowing and difficulty eating due to dental problems. Physical functioning was based on grip strength and gait speed; disability was assessed as mobility limitations. Frailty was ascertained using the Fried frailty phenotype. Cross-sectional analyses were undertaken using logistic regression. Results In the Newcastle 85+ Study, dry mouth symptoms, difficulty swallowing, difficulty eating, and tooth loss were associated with increased risks of mobility limitations after adjustment for sex, socioeconomic position, behavioural factors and co-morbidities [odds ratios (95%CIs) were 1.76 (1.26–2.46); 2.52 (1.56–4.08); 2.89 (1.52–5.50); 2.59 (1.44–4.65) respectively]. Similar results were observed for slow gait speed. Difficulty eating was associated with weak grip strength and frailty on full adjustment. In the TOOTH Study, difficulty eating was associated with increased risks of frailty, mobility limitations and slow gait speed; and complete tooth loss was associated with increased risk of frailty. Conclusion Different markers of poor oral health are independently associated with worse physical functioning and frailty in the oldest old age groups. Research to understand the underlying pathways is needed.