This dissertation examines the macroeconomic impact of reduced labor market friction on the U.S. business cycle after the mid-1980s. The first two essays investigate the relationship between labor market flexibility and macroeconomic stability from a post-Keynesian perspective. In the third essay which reviews the relationship between labor market flexibility and patterns of U.S. business cycle, I test the argument that after 1985 Okun’s coefficient became larger due to the flexible labor market. In essay 1, considering two aspects of labor market flexibility, employment flexibility and real wage flexibility, I adopt the flex-output model (Skott, 2015) to first discuss employment flexibility and then extend it by incorporating real wage dynamics induced from a wage-price Phillips curve (Flaschel and Krolzig, 2006) to address real wage flexibility. The simulation of model explains that employment flexibility increases instability of an economy whereas real wage flexibility reduces it. Empirical results of this paper suggest that during the Great Moderation, real wage flexibility played a major role in stabilizing the U.S. economy. On the other hand, employment flexibility has contributed to destabilizing the economy during the Great Recession. In essay 2, using structural VAR analysis, I provide more rigorous empirical evidence to support the hypothesis in essay 1—real wage flexibility played a major role in stabilizing U.S. economy during the Great Moderation, and employment flexibility has contributed to destabilizing the economy during the Great Recession. I found that during the Great Moderation (1) Employment and real wage flexibilities were operating simultaneously; (2) The employment flexibility was not so severe; (3) Flexible real wages functioned as an autonomic stabilizer; (4) Therefore, stabilized goods market during the Great Moderation can be explained by dominating effect of the real wage flexibility over the employment flexibility. For the Great Recession, however, severe asymmetry in the business cycle and the lack of observations obstructs reliable empirical work. In essay 3, I discuss the observations of increased cyclicality in aggregate hours and increased responsiveness of the (un)employment rate to output changes after 1985, which have contributed to recent debate about the validity of Okun’s law. To investigate this, I measure Okun’s coefficients in three phases of the business cycle—recessions, early expansions and late expansions. Related findings include: (1) The main determining factor for an increased coefficient for aggregate hours is the increased responsiveness of the employment rate during late expansions. (2) The increased responsiveness of hours per employee in early expansion is another main determining factor for more reactive aggregate hours. These findings conflict with the flexible labor market hypothesis that focuses mainly on firms’ firing behaviors during recessions when they incur less costs than previously.