The development of small and medium-sized enterprises is one of the priorities of the European Union. The business sector is an impellent of competitiveness of the EU economy in the world. Such companies are also of major importance for the economy of our country. After the Polish accession to the European Union small and medium-sized businesses in our country have received new opportunities coming from the rules of the common market. It is made the analysis on the role played by the sector of small and medium-sized enterprises in the market economy, as well as the analysis on the opportunities for small and medium enterprises after the Polish accession to the European Union. In this research, it is talked about the tax conditions which have an influence on the development and competitiveness of Polish enterprises (including analysis of tax deductions and exemptions). In addition, the author discusses the Polish government’s policy and the EU’s policy to support the development of this sector of business.