Permit to Work system is a documented system to control activities that are inherently hazardous and may cause incidents. The aim of this study was to evaluate performance of Permit to Work (PTW) system in an oil refinery. The Study was a cross-sectional study that was done during 2019 in one of the oil refineries in southern Iran. A total number of 125 participants who were experts that were working in an oil refinery and were in charge of Permit to work (PTW) issuing, were selected based on census method and were entered into the study. The instrument of this study was a questionnaire about evaluating performance of Permit to work system, which was completed by the participants after explaining the aim of the study and training them how to complete it. In order to data analysis SEPPTW software was applied. The results showed that the performance of Permit to work system in the studied refinery is generally in the moderate level (41.2 score). Also, in the field of hazard identification and risk assessment, the performance of Permit to work system was poor, but its performance in the field of coordination and informing was at a good level. Identifying the weak points and causes of defect in Permit to work system can result in increased levels of Permit to work system, and then reduced incidents from work related to permit to work in process industries.