INTRODUCTION:Rehabilitation of maxillary posterior region with endosseous implants is complicated in the presence of insufficient residual alveolar ridge and maxillary sinus pneumatization. New bone formation without any bone grafting materials has achieved promising results in sinus augmentation. Melatonin and hyaluronic acid suggest satisfying results in enhancing bone defect repair, osseointegration of dental implants. OBJECTIVES: To evaluate the effectiveness of melatonin and hyaluronic acid combination on bone regeneration in maxillary sinus augmentation. MATERIALS AND METHODS: 16 patients with missed maxillary posterior teeth indicated for sinus augmentation were divided equally into; group I, received melatonin and hyaluronic acid after sinus membrane elevation with simultaneous implant placement, and group II, did not receive any materials after the procedure. Clinical evaluation were done for pain, swelling, complications, and implant stability and radiographically for vertical bone height gain, bone density, and marginal bone level. RESULTS: There was a significant increase in bone density on the 1st and 6th months postoperatively in each group and between both groups (p ≤ 0.05). Regarding vertical bone height gain and implant stability, there was significant increase in each group, whereas the increase was insignificant between both groups. Marginal bone level difference between both groups was insignificant. Sinus membrane perforation occurred in one case only which did not affect the procedure completion; and there was no failure or complications along the follow up periods. CONCLUSION: Melatonin and hyaluronic acid could have a considerable properties regarding bone density in sinus augmentation without complications.