ObjectiveTo evaluate the reliability and validity of Guideline Implementation Success Assessment Tool (A-GIST). MethodsWith the guideline for the prevention and treatment of type 2 diabetes mellitus in China (2020 edition) as the target guideline, health care providers and patients from different hospitals across the country were investigated by questionnaire using A-GIST. Spearman-Brown coefficient and Cronbach's α coefficient were used to evaluate the split-half reliability and internal consistency reliability, while the structural validity, convergent validity and discriminant validity were investigated by confirmatory factor analysis based on structural equation. ResultsThe internal consistency reliability and split half reliability coefficients of the whole tool and each dimension ranged from 0.650 to 0.986. The scale-level content validity index (S-CVI/Ave) of content validity was 0.846. Confirmatory factor analysis showed that, the χ2/df of two sections of the tool were 8.695 and 6.123, respectively. The root mean square residual (RMR), the standard root mean square residual (SRMR) and the root mean square error of approximation (RMSEA) were under or almost under the threshold. Besides, the goodness-of-fit index (GFI) of them were 0.901 and 0.822, the adjusted goodness-of-fit index (AGFI) were 0.836 and 0.787, and the parsimonious normed fit index (PNFI) were 0.545 and 0.788, respectively. ConclusionGuideline Implementation Success Assessment Tool (A-GIST) was proved to be valid and reliable, and it shows that it is necessary to optimize the items under the dimensions of maintenance and evaluation of diagnosis and treatment effect in the future.