A series of experiments were conducted in a self-made smog chamber at (300 +/- 1) K and 1.01 x 10(5) Pa to simulate the photochemical reaction of ethyl methyl sulfide (EMS) and NO(x). The results showed that the higher the initial concentration of EMS, the more ozone was generated in the simulative reactions. It was found that the light intensity plays a very important role in the evaluation of ozone formation potential for EMS. The parameters of d(O3-NO) and IR (incremental reactivity) were used to quantify the potential of EMS on ozone formation. The obtained maximum IR values in this article for the five simulative reactions were 1.55 x 10(-2), 0.99 x 10(-2), 1.36 x 10(-2), 2.47 x 10(-2), and 1.65 x 10(-2), respectively. A comparison between the results we obtained here and the results we obtained previously for di-tert-butyl peroxide and acetylene showed that the potential reactivity of EMS on ozone formation was at a relatively low level.