In order to increase catalyst st bility and light olefins yield in catalytic cracking of naphtha, a series of HZSM-5 catalysts with various Phosphorous (0.2, 1.1 and 2 wt. %) and Cerium (2, 6 and10 wt. %) Loadings were prepared by co-impregnation method. The effect of Cerium and Phosphorous on the structure and acidity of HZSM-5 were examined by XRD, N2 adsorption/desorption and NH3-TPD. Also to study the amount of deposited coke the TGA analysis was done. The characterization results demonstrated that the structure of catalysts rarely changed by modification while the amount of acid sites increased. The results of cracking tests showed that the yield of propylene was significantly higher for Ce/P modified catalysts compared to parent catalyst while the ethylene yield did not change. Also increasing P loading the catalyst stability increased while increasing Ce loading resulted in higher propylene yield. At 680oC, the maximum Yield of ethylene and propylene were obtained about 16% and 36% respectively, for6%Ce-1.1%P/HZSM-5, while these yields showed no lost through 20 hours of reaction tests.These results revealed that there might be an optimum for acid density to maximize the Light olefins yield. In addition The TGA analysis indicates that the coke deposition is not a major factor for catalysts deactivation. So, catalyst deactivation might be attributed to the structural change.