The Fe-Mo/ZSM-5 catalysts were prepared by an impregnation method. A comparison of the catalytic activity for the reduction of NOx with ammonia over Fe-Mo/ZSM-5, Fe-ZSM-5 and Mo/ZSM-5 catalysts was carried out. Also, the effects of the conditions used for calcination as well as of the Fe/Mo ratio on the catalytic performance of Fe-Mo/ZSM-5 catalysts were studied. It was found that Fe-Mo/ZSM-5 is more active than Fe-ZSM-5 and Mo/ZSM-5 separately. Fe-Mo/ZSM-5 exhibited the best performance for SCR reaction with a Fe/Mo ratio of 1.5 and yielded the highest NOx conversion of 96% at a temperature of 430 degrees C. The results also showed that the performance of Fe-Mo/ZSM-5 is sensitive to the conditions used during calcination. The bulk phase and surface composition of the Fe-Mo/ZSM-5 catalysts were determined by XRD, BET, and XPS techniques, respectively. The results revealed that the surface Mo percentage is the largest when the Fe/Mo ratio is 1.5, which may be related to its higher activity for catalytic reduction of NOx. XRD results indicate that the best catalytic performance of the Fe/Mo = 1.5 sample results from a strong interaction among Fe, Mo and HZSM-5. In addition, it can be tentatively presumed that the surface nitrous species from the calcinations play an important role in SCR of NOx over Fe-Mo/ZSM-5 catalysts.