Abstract: A series of Pd-Au/Al2O3 catalysts modified by different amount of alkali metal K or Li were prepared by incipient wetness impregnation and characterized by low temperature nitrogen adsorption, FT-IR and H2-TPR techniques. The isoprene was used to evaluate the selective hydrogenation performance of the modified catalysts. The FT-IR results show that only Lewis acid sites exist on the catalysts, no Bronsted acid is found. The acid strength of K-modified catalyst is weaker than Li-modified catalyst. The H2-TPR results indicate that Pd-Au binary alloy is formed, the reduction peaks of catalysts shift to higher temperature after modified by alkali metals. The reaction results of isoprene selective hydrogenation on the modified Pd-Au/Al2O3 catalysts show that the isoprene conversion and isopentenes selectivity increase when addition of K2O. The LiO modification reduces the conversion of isoprene but isopentenes selectivity increases. At 70 ℃, isoprene conversion reaches 90.0%, isopentenes selectivity is 86.0% on the catalyst Pd-Au/Al2O3 with 1.2% K2O.