It has been reported that the operative treatment for the preservation of tooth having periapical lesion has shown over ninety percent of success whereas in the case where calcified canal is severe, canal is perforated, ledge is formed, tooth restored by post and core and cases where symptoms still exist after treatment, endodontic treatment may not all be the solution in attaining a successful treatment. Thus Apicoectomy would generally be used to prevent the loss of tooth having periapical lesion where treatment prognosis is poorly evaluated by endodontic treatment. In case 1 and 2, endodontic treatment was applied due to unilocular radiolucent lesion in periapical area but the symptoms somehow did not show improvement and therefore operated apicoectomy, and as in case 1, favorable results were attained but as in case 2, yet more observation has to be done. The followings are the results we have concluded : 1. In the process of endodontic treatment, absolute canal obturation has great effect on attaining successful treatment. 2. In cases where endodontic treatment is not highly recommended, for example, tooth having dental pulp and periapical lesion, favorable results can be attained by applying apicoectomy.