Background: In most cases the etiological factors of periapical diseases are oral contaminants through the root canal or degenerative pulpal tissues. Infections of the dental pulp occur as consequence of dental caries, operative dental procedures, trauma, and involve a mixed, predominantly gram-negative, anaerobic micro-organisms.Therefore the mere surgical removal of the periapical lesions without proper root canal disinfection and obturation will not result in the healing of the periapical tissues. So successful management and repair of periapical pathosis depends on complete debridement of the root canal system, followed by three-dimensional obturation to seal both the apical foramen and coronal orifice. Objectives: To find out clinical and radiological evaluation of non-surgical management of non-vital teeth with periapical pathosis by conventional root canal treatment. Methods: A total number of 50 infected teeth with periapical lesions were treated by conventional root canal treatment. This Experimental study was carried out for a period of 12 months from January 2019 to December 2019 in Shah Ali Dental Clinic, Dhaka, Bangladesh. Irritants from the root canal system was removed by mechanical instrumentation (Crown down Technique), chemical irrigation with Naocl and by using Calcium Hydroxide as intra-canal medicaments and fluid tight obturation both apically and coronally resulting repairs of inflamed periapical tissues. Depending on the extension of tissue damage repair varies from a simple reduction and resolution of the inflammation to a more complex regeneration involving remodeling of bone, periodontal membrane and cementum. Results: This study present 1 years clinical and radiological follows up period. Among 50 cases 40 cases could be treated as acceptable as their responses were good both clinically and radiologically and 7 patients came back with some complications among them 5 cases were uncertain and 2 cases were unacceptable. ..............