Construction development industry's principle objective is to guarantee that the schemesfinish on time inside financial plan, and accomplish diverseobjectives. Construction project endsinside spending plan, is basic worries in development the board, and imagined as most significant limitations for estimating achievement of any development venture. Budget overrun can be defined as the actual extra amount that is spenton a project than was planned in the budget. This budget overrun required extra financial expenditure. The root cause factors of budget overrun due to construction management and highlighted with reason and recommendation. The main objective of this study is to clarify the factors that causes budget overrun in construction project at Muscat, Khabourah, Bidbid, Musanah and Sohar cities in Oman. The quantitative analysis is carried out by interviewing construction experts working as consultant, contractors and project client in Oman via questionnaire. The collected data is analyzed by using average index method to determine the substantial factors causing budget overrun in construction projects.