Background: Mounting evidence has demonstrated a reciprocal association between diabetes mellitus and periodontal diseases, characterized by loss of alveolar bone, gingival recession and root exposure. Recently, studies showed that type 2 diabetes patients were at high risk to development root caries. This essay aims to clarify the relationship between root surface caries (RC) and periodontal parameters in diabetes patients, as well as evaluate relevant risk factors in Type 2 diabetes mellitus (T2DM). Materials and Methods: A total of 132 qualified adult patients with T2DM and periodontitis were recruited to this study. Radiographic data were collected to calculate alveolar bone loss (ABL). Subjects were assigned to three groups according to tertiles of ABL to make a comparison. Decayed and/or filled teeth (DFT) were calculated for both coronal and root surface as the caries indices of the remaining teeth. The plaque index (PLI), gingival recession (GR), probing depth (PD) at six sites per tooth, number of missing teeth, number of retained root remnants, and number of teeth with furcal lesions were recorded during clinical examinations. Blood analyses were carried out for glycated hemoglobin (HbA1c), fasting glucose. Correlation analysis, analysis of covariance (ANCOVA), and logistic regression were used to analyse the data. Results: By analyzing covariance, the research found that subjects with increased ABL have significantly higher numbers of missing teeth, root surface caries DFT, teeth with furcal lesions ( P <0.05). There is a significant positive correlation between root surface caries DFT and ABL, GR, coronal caries DFT ( P <0.05), respectively. ABL, coronal caries and age became significant predictor variables for Root Surface DFT (≥3)) ( P <0.05). Conclusion: Root surface caries were associated with ABL, GR and coronal caries in periodontitis with T2DM as well as ABL, coronal caries and age became risk factors for predicting the occurence of RC. Key Words: Association, Root Caries, Diabetes mellitus, Periodontitis