Background Vitamin D deficiency has been linked to the risk of frailty. However, there are limited methods for evaluations of the potential association of vitamin D with frailty in a longevous (80+) population. The aim of this study was to examine the association between plasma 25-hydroxyvitamin D [25(OH)D] levels and the risk of frailty among the Chinese community based oldest-old. Methods Secondary analysis of data compiled in the 2011 wave of the Chinese Longitudinal Healthy Longevity Survey (n = 1324) was performed. Frailty was assessed by the Study of Osteoporotic Fractures (SOF) index. Multivariate logistic regression and spline smoothing with threshold effect analysis were performed to investigate the association between 25(OH) D level and the risk of frailty after adjusting for socio-demographic variables, health characteristics and confounding biomarkers. Results The mean age was 92.89 +/- 7.92 years, and 844 (63.7%) participants were women. In all, data from 426 (33.2, 95% confidence interval, CI: 29.66-34.69) frail participants were recorded. After adjustment for confounding covariates, the level of 25(OH) D was significantly related to frailty. By spline smoothing with threshold effect analysis, a monotonically negative association between 25(OH) D and frailty was identified. Subgroup analyses revealed that the association did not differ by sex or age. Conclusions The 25(OH) D level was inversely associated with the risk of frailty among the Chinese community-based oldest-old.