This paper focuses on the research of the structural changes and its influence on the development of the knowledge economy. It reflects main theoretical aspects of the structural changes and the knowledge economy. Structural changes are considered as changes of expenditures on education and R&D, which are assumed as knowledge core – the primary and essential part of knowledge and of the knowledge economy. There are identified countries that have the closest position to the knowledge economy nowadays by the knowledge economy index, and, secondly, after examination of the structural changes of the national economies with emphasis on the knowledge sector, there is made a statistical evaluation of the influence of the knowledge core’s changes on the knowledge economy index (KEI). Consequently the purpose of the paper is to evaluate impact of the quaternary sector’s changes on the development of the knowledge economy, using the knowledge assessment methodology and analysis of the structural changes of national economy with emphasis on the knowledge core.