Heritage buildings, properties of all human kind, are still abandoned and ruined all over the world. Like many countries in Africa, most projects on restoration of heritage vi buildings in Ethiopia, are hampered by challenges that results in failures of undertaking the necessary works on cultural buildings and objects which makes the project to become unsuccessful. Previous inappropriate repair works, change of functions and natural conditions have imposed serious damage on Fasil Castles and Lalibela churches though the Community, GOE, UNESCO and World Monument Fund have already conducted restoration work on the site. On the contrary, there are few moderately successful restoration of heritage building projects like Ras Ginb and „Atatami Michael Church‟ in Fasil Castles. This indicates that, there exist some sort of factors which contributes to their successes/ failures of projects accordingly. The main aim of this study was to investigate the factors that affect the success of restoration of heritage building projects, and to prepare a call for action guidance. To achieve the objective, a mixed approach which deploys questionnaires and three case studies („Ras Ginb‟, „Kusquam Church & Mintiwab Palace‟ and „Guzara Palace‟) were conducted. A questionnaire survey was distributed (face-to-face & online) to seventy (70) respondents which were randomly selected from target groups and 64 questionnaires were returned. SPSS V24 software was used to analyze the results. Each case study provides considerable evidence that supports the study‟s conclusion. Success factors were ranked using descriptive statistics. Budget allocation ranked the first, followed by sourcing/ availability of original material-second, commitment of client, consultant and contractor-third, top management support-fourth, and competent contractor and consultant ranked the fifth. Function/adaptive reuse, quality, authenticity/originality, cost/budget, and time/ schedule are success criteria ranked from first to fifth. The scope of the research was limited in space, time and topic. It was limited in Amhara region at Gondar and Bahir Dar, and Addis Ababa. This study will be expected to have a contribution to cultural and heritage concerned offices, Project Management Body of Knowledge (PMBOK), and vital for students, lecturers & researchers. Key words: heritage, historical, buildings, restoration, success factors, success criteria, authenticity, adaptive reuse, performance.