NaY zeolite catalysts with and without potassium salt modifications were studied with respect to dehydration of lactic acid to acrylic acid. The selectivity for acrylic acid could be dramatically enhanced by modification of the NaY catalysts with potassium salts. The KI-modified NaY catalyst exhibited the best catalytic performance for lactic acid dehydration, over which 97.6% conversion and 67.9% acrylic acid selectivity could be gained at 598 K. Characterizations with TGA, XRD, N-2 adsorption, Al-27 MAS NMR, XPS, NH3-TPD, CO2-TPD, and mechanism analysis revealed that the counteranions in potassium salts exerted a significant influence on the catalytic behaviors via an electronic effect.