Introduction: Antioxidant agents such as cocoa could have some benefits in treatment of inflammation including periodontitis. The aim of this study was to investigate the effects of cocoa consumption on moderate chronic periodontitis. Materials &Methods: This single-blind randomized clinical trial study was performed on 40 subjects who were randomly divided into two groups. Treatment group received 30 gr dark chocolate (78% cocoa) and control group received 22.5 gr white chocolate three times a day for 4 weeks. Saliva samples were collected from patients at baseline and t wenty-eight days after eating chocolate. Probing pocket depth (PPD), Gingival index (GI, Silness and Loe), Modified papillary bleeding index (MPBI, Barnett), Clinical attachment loss (CAL) were recorded at baseline and 2nd, 4th, 6th, 8th weeks later in ramfjord teeth. Total antioxidant capacity (TAC) and lipid peroxidation of saliva were estimated by Ferric reducing antioxidant power (FRAP) and Tiuborbituric acid reactive substances ( TBARS ) methods. Data of clinical parameters were analyzed using t-test and repeated measures test. Biochemical parameters were analyzed using t-test. Results: Intra-group comparison of clinical parameters demonstrated significant decrease in both groups (p<0.0001) and inter-group comparison showed significant decrease of MPBI in treatment group, (p<0.03). MPBI and GI were significantly decreased in treatment group compared to the control in the weeks of 4th, 6th and 8th, according t-test ( GI4, P=0.008-GI6, P=0.008-GI8, P=0.009), (MPBI4, MPBI6, MPBI8, P<0.0001). Treatment group showed the increase in FRAP, (p<0.00001 ) and decrease in TBARS, ( P<0.015) which were statically significant in compare with control group. Conclusion: Consuming dark chocolate could increase TAC and decrease lipid peroxidation, gingival bleeding and inflammation.