One indicator of a successful construction project is the timely completion of the project according to planning. However, delays in construction projects have now grown a commonplace. Many contractors are unaware of unable to predict the potential time delays. Thus, delays in construction projects are difficult to avoid. The biggest impact of time delays is financial losses for various parties involved in the project. This research aims to determine the factors that have a significant influence and the relationship between factors in time delays in multi-storey building construction projects in Indonesia. Data collection was carried out by distributing questionnaires. The respondents in this study were fifteen experts who had experience in the construction sector. The factors causing time delays in this research will be analyzed based on the principles of professionalism and ethics in work. The factors causing time delays are divided into twenty factors. This research uses the Interpretive Structural Modeling (ISM) analysis method. ISM is a method that can describe the structure of complex systems through graphics and words. Through data analysis, it was found that the factors that had the most significant influence on construction project delays in Indonesia. The factors that are the most influential causes are: Through the results shown, time delays in construction projects in Indonesia can be prevented with professionalism and work ethics, specifically having a good work plan and having experienced skilled workers.