Aim This study aimed to compare the effects of local and systemic metronidazole in patients with chronic periodontitis. Materials and methods In this randomized clinical study, 30 patients (3 teeth per patient) were treated in three groups: SRP treatment alone, metronidazole tablet as adjunctive treatment, and metronidazole gel as adjunctive treatment. BOP (Bleeding on probing), PPD (pocket probing depth), and CAL (clinical attachment level) data were taken at the beginning and three months later. Collected data tested by Wilcoxon test and Kruskal-Wallis. Statistical analysis was performed using SPSS V.21. Results BOP, CAL, and PPD levels were significantly different at the beginning of treatment and after three months, and this was true for all treatments. BOP, CAL, and PPD levels did not differ significantly between the three groups after the treatment. (p > 0.005). Conclusion The effectiveness of these methods was all equal. Accordingly, choosing one of these methods depends on the ease of use, the patient's condition, and the clinician’s opinion. Clinical relevance: Chronic Periodontitis is progressive disease wich can cause tooth loss. The accepted treatment is scaling and root planing (SRP). Antibiotics used systemically can penetrate the depth of the periodontal pockets but have several side effects; Hence, using a kind of less complicated medicinal form in the form of a topical gel as an adjunctive therapy in the treatment of chronic periodontitis can be more effective.