Background: Today, oil, gas, and petrochemical industries are of strategic significance in the macro-development of oil-rich countries. These industries, given the nature of the work and the technical complexity of the various processes, are hazardous and susceptible to occupational accidents. More than 90% of the accidents are related to the faults and unsafe actions of personnel, either directly or indirectly. Objectives: The aim of this study is to investigate the unsafe actions of staff working in the maintenance unit of a petrochemical complex. Materials and Methods: This is a descriptive and analytical study conducted on 167 morning-shift workers at the Mahshahr petrochemical complex. The data were collected based on a checklist of unsafe actions prepared through a direct observation of their activities and an analysis of work instructions, documents, and incident reports. SPSS statistical software was also used for data analysis and relevant testing. Results: According to the results of this study, the mean number of unsafe actions performed by the employees was 42%. The highest number of unsafe actions achieved in the maintenance mechanical unit was 52.8%, 47.1% in repair services, and 43.8% in machinery. The highest frequency of unsafe actions were caused by indiscretion and negligence, a failure to use a face shield and goggles, and noncompliance with safety principles. Conclusions: According to the findings, there has been a rise in the number of unsafe actions in machinery and maintenance service units compared to other maintenance units. As such, training courses based on the behavior-based safety principles at the beginning of employment, close monitoring of health safety environment (HSE) officials on the implementation of regulations, and provision of appropriate scheduling based on weather conditions and the nature of maintenance services are recommended. In addition, a refrainment from hastiness in performing duties, enhanced participation from the employees to improve occupational safety, and the production and distribution of high-quality personal protective equipment (PPE) is also recommended to mitigate unsafe actions.