Objectives <p>To evaluate the clinical and microbiological effects of a gel containing green tea and hyaluronic acid (GT/HA) following open-flap debridement surgery in comparison with those of a chlorhexidine-based gel.</p> Materials and methods <p>This randomized, controlled, double-blind, noninferiority trial included 38 patients with stage 3 periodontitis. After undergoing surgery, participants were randomly assigned to receive either GT/HA gel or chlorhexidine gel three times daily for 14 days. Clinical parameters (plaque index, probing depth, bleeding on probing, and clinical attachment level) were evaluated at baseline and 60 days postoperatively. Subgingival biofilm samples were collected at baseline and after 14 and 30 days and analyzed using checkerboard DNA–DNA hybridization for 40 bacterial species. Patient-reported outcomes included postoperative pain, analgesic consumption, and quality of life assessed by the OHIP-14 questionnaire.</p> Results <p>Both groups showed statistically significant clinical improvements from baseline to 60 days, with no significant differences between treatments. Temporary reductions in some bacterial species were observed during the 14-day gel application period in both groups, followed by regrowth after discontinuation. GT/HA gel was associated with fewer adverse effects, particularly regarding taste alteration and tooth or tissue staining. A reduction in OHIP-14 scores was observed in both groups, with statistically significant differences between baseline and 30 days after surgery.</p> Conclusions <p>GT/HA gel was noninferior to chlorhexidine gel in terms of clinical and microbiological outcomes and showed greater patient tolerability.</p> Clinical relevance <p>GT/HA gel may represent a safe and effective alternative to chlorhexidine in postoperative care in periodontal surgery.</p>