A series of KNO3 modified zeolite catalysts（K/Zeo，Zeo = ZSM-5 , Y）were prepared in impregnation method and employed in the conversion of lactic acid to 2, 3-Pentanedione(PDO). The characterizations of XRD and low-temperature N2-physisorption indicated that the process of KNO3 modification damaged to some extent the framework of zeolites, resulting in the decrease of specific surface area and pore volume but the increase of the pore size of the zeolites. The catalytic performance evaluation and carbon balance examination have shown that, compared with those over the unmodified zeolite catalysts, both PDO yield and carbon balance are greatly improved, due to the generation of new active sites and the adjustment of pore sizes, over the modified ones. Among various modified catalysts, a K/NaZSM-5(60), which possesses a micro-mesoporous structure, exhibits the best performance, providing 52.4% lactic acid conversion and 48% PDO selectivity at 280 ℃. The high performance of this catalyst may be the result of its large specific surface area.