Introduction: System integration can be achieved in a number of ways and at different levels. In practice all management systems are mutually coordinated systems functioning almost independently. Integration enables synergetic effect and optimum workplace performance on all aspects of Safety, Health, Environment and Quality. Aim of work: To evaluate the effect of Occupational Health, Safety and Environmental Protection Management System (HSEMS), integrated audit on Health, Safety and Environmental (HSE) protection performance level of petrochemical companies. The study was designed to evaluate the compliance degree of the organization with International Standardization Organization for environmental management, (ISO 14001) and Occupational Health and Safety Administration Series (OHSAS 18001) requirements in five petrochemical companies to ensure continued effectiveness and efficiency. Materials and methods: Performance indicator checklist and a questionnaire were designed to be used as a tool for internal review of HSE directed by OHSAS 18001:2007 and ISO 14001:2004. Relevant data were collected and statistically analyzed. Data collection was performed through various methodologies such as reviewing HSE published documents, safety reports of the companies, conducting interviews and surveys among HSE managers. Results: The study indicated that there was a gap between the effectiveness of HSEMS before and after the integrated audit by about 17.8 % at company A, 18.3 % at Company B, 21.5 % at Company C, 31.5 % at Company D, and 10.1 % at Company E. Factor analysis indicated that there was an identity and good correlations between the HSE performance indicators means for all companies. The results after integrated audit on the studied companies were categorized by a SWOT analysis technique to four areas of strength, weakness, opportunities and threats. Conclusion: Although the performance of health, safety and environment at the selected petrochemicals companies seems to be at a high level, the underlined study revealed some weaknesses and threats that affect the efficiency of HSEMS. However, HSE performance indicators were not enough to evaluate the effectiveness of HSEMS. The integrated audit technique is very important to evaluate the effectiveness of HSEMS.