This study aimed to assess the use of doxycycline in adjunct to periodontal therapy on the glycemic levels for chronic periodontitis patients with type 2 diabetes mellitus (DM). Fifty-one diabetic subjects with chronic periodontitis were selected and randomly assigned into 3 groups with 17 subjects each. Scaling and root planing (SRP) was done in group I, SRP and doxycycline was given in group II, and group III did not receive any periodontal treatment till 3 months. Probing pocket depth (PPD), clinical attachment level (CAL), plaque index (PI), gingival index (GI), and metabolic parameters were evaluated at baseline (day 0) and after 3 months (day 90). The statistical analysis was carried out using SPSS 17.0 software with significance fixed at 95% CI (p < 0.05). The mean difference between baseline and day 90 for all periodontal parameters was significantly higher (p < 0.01) in group I and group II compared to control (group III). The metabolic parameters such as fasting plasma glucose (FPG), 2-hour postprandial plasma glucose (PPG), and glycated hemoglobin (HbA1c%) level were reduced in groups I and II compared to group III; however, only HbA1c% values were found significantly reduced (p < 0.01) at day 90. Group II showed significantly better metabolic parameters than group I at day 90. The adjunct of doxycycline to conventional periodontal therapy provides additional benefit in reducing glycemic level and improves periodontal health. The prevalence of diabetes as well as periodontitis is increasing nowadays in the world. With treatment of periodontitis, it is found that there is reduction of glycemic level in diabetes. So it is an alert to health professionals about the relation of diabetes and periodontitis and so that they conduct a multidisciplinary treatment.