Abstract: The mechanism by which chronic periodontitis (CP) affects type 2 diabetes (T2DM) remains unclear. Therefore, the aim of this study is to evaluate the effects of periodontal therapy (PT) on the glycemic control and adipokines of patients with T2DM and CP with the purpose of elucidating the possible mechanisms by which CP influences T2DM. Forty-four patients with T2DM and CP were randomly divided into two groups according to whether they underwent PT. Periodontal status, blood glucose, and the levels of serum tumor necrosis factor α (TNF-α), interleukin-6 (IL-6), adiponectin (APN), and fibroblast growth factor-21 (FGF-21) were measured at baseline and after 3 months. The results revealed that the probing depth (PD) and attachment loss (AL) were significantly improved, the serum levels of TNF-α and IL-6 were significantly decreased, and APN and FGF-21 exhibited substantial increases in the intervention group after 3 months (p < 0.05), whereas no significant changes were observed in the control group. The glycated hemoglobin (HbA1c) levels in both groups decreased significantly after 3 months compared with baseline (p < 0.05), but the intervention group exhibited a significantly greater change (p < 0.05). In conclusion, PT may relieve periodontal inflammation, which causes a reduction of insulin-antagonizing adipokines and an increase in insulin-sensitizing adipokines, thereby eliciting an improvement in glycemic control.