Objective@#To investigate the relation between serum markers, the degree of lesions and the active period of chronic periodontitis in patients with type 2 diabetes mellitus.@*Methods@#A total of 595 patients with type 2 diabetes mellitus were selected, and oral examinations and laboratory tests were conducted. The patients were divided into a periodontally healthy group mild, moderate and severe periodontitis groups depending on the diagnostic criteria for chronic periodontitis. The patients were also divided into periodontally healthy, resting and active groups depending on the diagnostic criteria of the active period. The relationships between serum biochemical indices, the degree of lesions and chronic periodontitis activity were analyzed. @*Results@#The prevalence of chronic periodontitis in patients with type 2 diabetes was 74.6%, and the proportions of patients with mild, moderate, and severe chronic periodontitis were 44.9%, 16.1% and 13.6%, respectively. The composite ratio of active periodontal chronic periodontitis was 33.1%. Compared with the patients in the control group, the fasting plasma glucose and HbA1c levels were more poorly controlled in the type 2 diabetes mellitus groups with chronic periodontitis (P < 0.05). There were significant differences in fasting blood glucose levels between mild periodontitis group and moderate, severe periodontitis group (P < 0.05). There was no significant difference in HbA1c levels among the mild, moderate and severe groups (P>0.05). However, there were significant differences in fasting blood glucose levels between the groups with various degrees of progression in the following order: active (11.24 mmol /L) > resting (9.64 mmol/L) > control (8.82 mmol/L) (P < 0.05).@*Conclusion@#The severity of chronic periodontitis plays no role in the level of HbA1c, instead, the level of fasting plasma glucose changes with the severity and progression of chronic periodontitis.