This article is to analyze the reasons of the failure of democratization and economic liberalism in Poland in the interwar period. Poland had failed to establish assembly democracy and a liberal market economy system, which allowed the Pilsudski's coup d'etat and etatism (economic interventionism of the state) to become dominant. This article will attempt to show why the Polish liberal economic policy collapsed and what political and economic conditions were instrumental to the rapid growth of authoritarianism by analyzing not only the economic aspects but the relationship between the parliament, government and president, etc. The economic liberalization and democratization tried out in newborn Poland successively failed due to the immature political bodies, conflict among the parliament, president and government, and the immature market. The administration established after the coup d'etat of Pilsudski was backed up by the worldwide economic recovery and stabilized economic situations of the mid twenties, but not able to take any effective measures against the world financial crisis post 1929. During the 20 years of the interwar period, economic liberalism was always in the mainstream of economic policy, but there was no positive and strong ideology in the background of the appearance of etatism. The market was too feeble to support the unstable Polish economy, and under those conditions, strong intervention by the state in the economy could not be avoided.