Economic policy uncertainty affects firm dynamics and profitability, and thus imposes an impact on firm markups and market power. Using quarterly data of the U.S. publicly listed firms over 1985Q1 to 2020Q3, this paper empirically shows a decline of firm markups under an uncertain environment. However, the decrease in average markup does not necessarily imply an increase in market competition due to the heterogeneous effects among firms. Specifically, an uncertain environment seems to advantage larger and more innovative firms compared with smaller or less innovative firms, indicating a disproportionate distribution of resource and market power reformation. We further show that the within industry markup dispersion, as well as the market concentration, increases given one standard deviation increase of economic policy uncertainty.