<bold>Background:</bold> There is growing evidence that an antioxidant diet is a protective factor against frailty. However, few studies have examined the effect of comprehensive dietary antioxidants on frailty symptoms. The aim of this study was to examine the relationships between the composite dietary antioxidant index (CDAI) and frailty and the underlying mechanisms involved.<br /> <bold>Methods:</bold> Based on the National Health and Nutrition Survey (NHANES) 2003- 2018, this study included 11,277 older persons aged >= 60 years. In this study, frailty was defined as having a total score > 0.21 on the 49-item frailty index. Six dietary antioxidants were selected for use in calculating the CDAI. A weighted multiple logistic regression model with subgroup analysis and restricted cubic splines (RCSs) were used to examine the association between the CDAI and frailty. To examine the role of oxidative stress, mediation analyses were also conducted.<br /> <bold>Results:</bold> The association between the CDAI score and frailty risk was significant according to the multivariate model. Compared with participants in tertile 1, participants in both tertile 2 and tertile 3 had lower odds of developing frailty symptoms (OR=0.86; 95% CI=0.75- 0.97; P=0.02; and OR=0.81; 95% CI=0.70- 0.93; P=0.003). According to the subgroup analyses, the differences in interactions were not statistically significant. There was also a potential nonlinear relationship between the CDAI score and frailty risk. The serum albumin concentration and uric acid concentration had significant mediating effects on the association between the CDAI score and frailty index, with 19.25% (P=0.002) and 21.26% (P < 0.001) of the total, respectively.<br /> <bold>Conclusion:</bold> Frailty is negatively associated with the CDAI score, which may be partially mediated by oxidative stress.