The purpose of the article is to examine the chosen determinants influencing the capital structure in groups of micro, small and medium-sized enterprises. We tested if: company size, industry, tangible assets, has an impact on debt ratios. We employed two debts ratio: share of total and interest debt in capital. The study was conducted on the basis of 12 thousand SME financial statements. The inference was carried out with using ANOVA test and correlation. It was confirmed that micro, small and medium company’s capital structure affects the size of the company, the ‘material character’ of its assets and industry affiliation.