 The aim of this study is to verify the efficacy of Photodynamic Therapy PDT as an adjunct to non-surgical treatment of chronic periodontitis by assessing clinical and microbiological and immunological parameters. This is a randomized, controlled, double-blind, parallel clinical trial. Thirty eight patients with chronic periodontitis will receive conventional periodontal treatment. After eight weeks, patients will be re-evaluated and sites with residual pockets PD 5 mm will be selected as experimental sites, and will be allocated to test and control group randomly. The test group will receive the application of PDT and the control group will receive sham procedure. The clinical parameters will be evaluated at baseline, 3, 6 and 12 months after treatment. Subgingival plaque will be collected before PDT, a week after, 3, 6 and 12 months later. The microbiological evaluation will detect and quantify periodontal pathogens such as Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola and Aggregatibacter actinomycetencomitans with real time-PCR. During follow-up, patients will receive periodontal maintenance every 3 months, as well as the application of PDT or sham 