The main goal of this article is to analyze the level of differentiation of awareness and knowledge among managers of small, medium and large enterprises in the scope of the essence and meaning of intellectual capital as well as the influence of its elements on the sustainable development of enterprises in Poland. Intellectual capital is perceived as a key resource of an enterprise. It is also one of the most valuable resources of an enterprise, which enables its sustainable development. It is critical base of organization’s innovative and strategic sustainability. This article is based around the results of a survey conducted in 2019 among 1,067 enterprises operating in Poland. For the purposes of the verification of the statistical hypothesis, the classical chi-squared test of independence has been applied along with the analysis of variations for fuzzy numbers (FANOVA) with an assumed level of significance α = 0.05. The assessment of the influence of the elements of intellectual capital on the sustainable development of enterprises has been conducted with the application of fuzzy conversion scales. In fuzzy conversion scales, points are most often expressed as triangular or trapezoidal fuzzy numbers. The conducted research indicates a difference between theory and practice in the field of intellectual capital management among enterprises in Poland. On the one hand managers declare awareness of the importance of the influence of intellectual capital on the development of enterprises in Poland, whereas on the other hand, a significant majority of them state that they have not implemented an intellectual capital management strategy at their enterprises and neither identify nor measure this capital or its elements.