Construction project is a competitive business with high risk especially in developing countries like Iran which faces with many problems such as delay and time and costs increases. Thus, the first priority here is to determine the causes of prolongation of construction projects and to evaluate their importance. Khuzestan Steel Company (KSC) has made important contribution to the projects in Iran and in turn is required to finish them on time. In this study, an attempt was made to investigate the causes of delay in implementation of construction projects held by this company. Data was collected through questionnaire distributed among the sample including 10 owners, 10 consultants and 15 contractors. Accordingly, participants rated the causes in the questionnaire so the most important priorities of each area were specified using TOPSIS method. The results showed that according to the employers, consultants and contractors' viewpoints, the most important reason for delays in construction projects of KSC is related to the financial matters. Hence, according to the results obtained, causes for delays in the company's projects are largely related to the drilling permits and long administrative cycle to renew them. Besides, continuous production of steel in this company is another reason to delays of construction projects.