Delays are one of the biggest problems facing by the construction industry. The delays in construction projects have significant financial and social impact to all parties involved in the projects. The aim of the paper is to analyse the impact of delay in Libyan construction projects by identifying and ranking the delay factors. A comprehensive literature was conducted to build up the general knowledge required to identify the potential delay factors in different countries. A semi structured questionnaire was designed using literature and distributed to construction companies that were selected randomly. The delay factors were ranked using the frequency of occurrence and severity scale. The survey result exposed that the construction projects in the developing countries suffer more delay than the developed countries. The critical delay factors found in Libyan construction projects were low skills of manpower, changes in the scope of the project, slowness in giving instruction, poor qualification of consultant and delay in delivering site project to contractor. Statistical experiments including, Paired Samples T-Test, was run to test the significance of the survey data and found that the result was significant. A case study of Libyan building project was analysed to identify the possible project delay and the sensitivity of each delay factor using@ risk simulation program. The case study result found that the project might be delayed by 97 to 103 days for one block in comparison to the planned duration. The results will guide the construction manager to take necessary measures to reduce the impact on construction project. The outcome of this study provides a methodology for identifying the delay factors and analysing the impact on construction projects.