Building construction has been one of the fastest-growing segments of the construction industry inrnEthiopian. But most of construction projects, especially which are undertaken by local contractors werernpoor in accordance with time, cost and quality. Even though there are numerous factors, which affect thernbuilding construction projects, this research is aimed to assess and study four critical success factors,rnwhich influence success of building construction projects. Namely: Time, cost, quality, and projectrnmanagement competency. The four critical factors were identified from the widespread application ofrnproject management concepts and general understanding amongst practitioners. And twenty-fivernconstruction projects were selected as unit of analysis for this study.rnDescriptive research design was used to assess the critical success factors in the selected constructionrnprojects. Primary and secondary data were also used for the achievement of the study. A structuredrnquestionnaire was developed to gather information to assess and analysis the critical success factors,rnwhich affect the success of building construction projects. And other significant project managementrnpractices were also captured in relevant literature. Seventy-five questioners were distributed and onlyrnfifty-five of the respondents were responded the questionnaires. Then the data obtained from therndistributed questionnaires was analyzed using SPSS 24 software. Descriptive statistics were used tornanalyze and interpret the data found from the respondents. The findings show that the assessment of thernpractice level of the identified factors within the building construction companies resulted in a high levelrnof mean score values. And all the factors that are considered as critical success factors (project managerrncompetency, time, cost, and quality related factors) have a great contribution to the successfulrncompletion of a project and are being practiced within the companies under study. And from all thernidentified success factors, project manager competency related a critical success factor has the highestrnmean value. So the research recommend for building construction companies to emphasis more on therncompetency of their construction project manager. So that they can resolve cost, quality, and timernrelated problems.