OBJECTIVE: In this case, it is aimed to present non-surgical root canal treatment and rapid healing of mandibular second molar tooth with chronic apical periodontitis with furcation lesion. CASE: A 33-year-old female patient who did not have any systemic disease was admitted with the complaint of pain in the left lower posterior region. Clinical examination revealed a deep caries in the left mandibular second molar, pain on percussion, tenderness on palpation, and mobility. It was decided to take cone beam computed tomography (CBCT) in order to determine the size of the lesion in the relevant area. CBCT examination revealed a large periapical lesion and furcation lesion in the left mandibular second molar. Root canal treatment of the related tooth was began. After root canal preparation, calcium hydroxide was placed in the root canals and closed with temporary filling. Two weeks later, calcium hydroxide was removed from the root canals and filled using the lateral condensation technique. Coronal restoration was completed with fiber-containing composite (Every X flow). RESULTS: As a result of a short-term follow-up of 6 months, it was observed that the involved tooth was asymptomatic and the periapical and furcation lesion completely healed. In this case report, it has been shown that large lesions can be healed in a short time with non-surgical endodontic treatment with correct diagnosis and treatment planning.