This research examined factors affecting the implementation of the competency-based curriculum in public secondary schools in Mogadishu, Somalia. Specific objectives of the study were teacher professional development, principal’s supervision, and instructional materials. This research used a purely quantitative approach to analyze the data of this research. The data investigated in this study were collected from 292 academic staff randomly selected from six public secondary schools in Mogadishu, Somalia. The Cronbach’s Alpha coefficient was .726 obtained indicating that the instrument was reliable to collect data for this study. To analyze the data multiple regression analysis was used to find out the amount of gradient equated to the size of the bivariate correlations between the different predictor variables (principal’s supervision, teacher’s professional development, and instructional materials) and implementation of the competency-based curriculum. As indicated that there exists a strong, significant, and positive relationship between teacher professional development, as indicated by a factor, (r=.773, P=0.000<0.05.), principals supervision as indicated by a factor, (r=.622 with P=0.00<0.05), instructional materials as indicated by a factor, (r= .647 with p= 0.000<0.05.) and implementation of a competency-based curriculum. According to the result of this study, it is recommended that administrators of public Secondary schools and the Ministry of Education should ensure that all public schools have adequate teaching and learning materials and also should give training to teachers and supervise how to implement the school curriculum.