Objective: Evaluation of effects of simvastatin gel in combination with allograft on improvement of clinical parameters and bone fill in furcation involvement grade II mandibular molars compared to allograft alone. This randomized clinical trial is double blind and accomplished on ten patients with chronic periodontitis. Inclusion criteria: a pair of first or second mandibular teeth bilaterally with furcation involvement class II that have at least 3 mm horizontal penetration of probe in furca. At least 2 mm keratinized gingiva. Exclusion criteria: smoking; history of systemic disease; pregnant or breast feeding females; history of antibiotic consumption within 2 months; history of periodontal treatment within 6 months; history of hypersensitivity or treatment with statin; aggressive periodontitis; mobility grade 3; pulp pathology of teeth and poor oral hygiene. CBCT are taken and clinical parameters with probe in furca are measured. Following clinical parameters are measured at baseline and 6 months post-surgery: plaque index, bleeding index, recession, probing depth, and clinical attachment level, horizontal and vertical depth. After local anesthesia, full thickness incision with maintenance of keratinized gingiva was done. Then, reflect the flap and debridement. Measurement of horizontal and vertical bone loss is repeated and recorded. In test group, allograft bone chips combined with patient blood and simvastatin gel are put in furcation defect. Then, the defect is covered with allograft membrane. After early healing of soft tissue, surgery is done on the control side. Allograft bone chips with blood and placebo gel are put in the defect. Similar to test group, other steps of operation were done. During monthly visits, plaque and gingival index are recorded due to maintain optimal patient’s hygiene. In after 6 month visit, clinical and radiographic parameters are reevaluated and recorded.