Mirmohammadi, M., Ibrahim, M.H., Ahmad, A., Kadir, M.O.A., Mohammadyan, M., Mirashrafi, S.B. View Correspondence (jump link) aSchool of Industrial Technology, University Sains Malaysia, 11800, Pulau Pinang, Malaysia bDept. of Occupational Health, Faculty of Health, Mazandaran University of Medical Sciences, Mazandaran, Iran Abstract Objectives: To determine the risk assessment of diisocyanate for workers and HDI concentration in the indoor air. Methodology: For air monitoring 100 air samples were obtained using National Institute of Occupational Safety and Health (NIOSH) 5522 and for biological monitoring 50 urine samples were collected from the workers and analyzed with using William's biological analysis method. Results: The results showed high maximum concentration of hexamethylene diisocyanate (more than 88μg/m3) when compared to the NIOSH standard and high concentration of hexamethylene diamine in the worker's urine. Conclusions: Multiple regression models were obtained to predict of HDI risk in the polyurethane factories.