---

Background: Xylene is known as one of the most toxic of the nervous system. The purpose of this study is to estimate the concentration of xylene in the cabin of the vehicles production in Iran. Also the effect of ventilation, cigarette smoking, and air freshener inside the vehicle, fuel type and car decorations on the concentration of the substance being studied.  Methods: 152 vehicles Pride and 44 vehicles Thunder 90 of the Iranian cars were selected for sampling. Samples were collected with activated carbon tubes and were analyzed using gas chromatography with mass detector. Other information was collected using a checklist. Findings: The mean concentrations of xylene in Pride and Thunder 90 vehicle was respectively 657/4± 1416/3 and 252/5± 643/06 µg/m3. Concentration of the substance in the Pride cars is almost double Thunder 90 cars. Concomitant use of petroleum and natural gas (CNG) in vehicles increases the concentration of xylene. Effect of parameters such as type of vehicle air conditioning system, cigarette smoking, and air freshener inside the car, the car's interior trim car had no significant influence on the concentration of xylene. The only type of fuel used had significant influence on the concentration of the substance inside the car. Conclusion: xylene is volatile organic compounds were found in the cabin of the vehicle. Average xylene measured in this study was lower than the standard in Hong Kong, but it was more than the standard NIAQS in China.