Objective: To compare the effectiveness of newly developed tetracycline hydrochloride gel (TCN) to that of scaling/root planing (SRP) in treatment of recurrent sites in maintenance periodontal patients. Methods: Nineteen periodontal maintenance patients with recurrent sites (pocket depth >5 mm with bleeding on probing) were included in this study. Patients were randomly divided into 2 groups, i.e., TCN (12 sites) and SRP (15 sites). TCN was applied to active sites without mechanical instrumentation. Clinical parameters including probing depth (PD), clinical attachment level (CAL), bleeding on probing (BOP) and microbiological parameter (total anaerobic bacteria count) were measured at baseline, 1, 4, 8 and 12 weeks after treatment. Results: At baseline, PD and CAL of TCN group were 7.25±1.6 and 7.83±1.59mm, respectively. SRP group demonstrated PD and CAL of 6.87±2.13 and 7.93±3.26mm, respectively. After treatment, TCN group showed significant improvement in PD, CAL, and total bacterial count from week 1 to week 12 (p<0.05). SRP group demonstrated significant reduction of PD only after 1 to 8 weeks. Total bacterial count in SRP group reduced significantly after week 1 until 12. However, significant CAL gain in SRP group was observed only at 1 week after treatment. When compared all parameters between TCN and SRP groups at each time, there were no significant differences between groups. Conclusions: The newly developed TCN gel was equally effective to SRP in treatment of recurrent periodontitis. Therefore, TCN gel may be used as an alternative treatment in recurrent sites in maintenance patients. This study was supported by Internal Grant, Faculty of Dentistry, Chiang Mai University.