OBJECTIVE: This study investigated the relationship between frailty and quality of life in middle-aged and older adults, and determined how age influences the relationship between frailty and quality of life. DESIGN: A cross-sectional study from Korean Longitudinal Study of Ageing (2006-2020). SETTING AND PARTICIPANTS: There were a total of 9301 participants aged ≥45 years at baseline (2006). METHODS: Frailty was assessed using the Korean Frailty Instrument, which categorized participants as non-frail, pre-frail, or frail. Quality of life (QoL) was measured using a visual analog, ranging from 0 (worst) to 100 (best) in 10-point intervals. We used multiple linear mixed models to examine the association between frailty and QoL among middle-aged and older adults and to test the interaction effect of frailty status and age on QoL. RESULTS: Of 9301 participants, 53.7% were non-frail, 30.3% were pre-frail, and 16.0% were frail. Average QoL scores were 68.7 in the non-frail group, 59.9 in the pre-frail group, and 48.2 in the frail group (P <
.001). The linear mixed model analysis showed that pre-frail (β = -2.235, SE = 0.152, P <
.001) and frail (β = -5.072, SE = 0.269, P <
.001) individuals had lower QoL scores compared with non-frail individuals. Although QoL scores remained stable across age groups in non-frail individuals, those with frail status showed an increase in QoL with age. CONCLUSIONS AND IMPLICATIONS: Frailty is significantly associated with lower QoL in both middle-aged and older adults. In addition, the interaction of age and frailty showed that QoL improves with age in frail people. This suggests that the impact of frailty on QoL is greater in middle age.