The quality management system according to ISO 9001: 2015 is the most recognised standard of business in the world. By adopting its requirements, any business organization can implement such a measure in its industry. The most important determinant of the quality management system according to ISO 9001: 2015 is the leadership commitment. The main objective of the research was to examine the degree of leadership commitment. The study was conducted on the leadership of micro, small, medium and large business organizations. A total of 600 business organizations were contacted, and a total of 269 questionnaires were completed in the end. In addition to the survey, other scientific methods were used, mainly in processing the collected data. The research has shown that there is a high degree of leadership commitment, relying on ISO documentation and performing internal audits most often only once a year, which is the minimum standard requirement. It has also been proven that there is a statistically significant difference in leadership commitment between business organizations of different sizes. In medium and large-sized business organizations, there is a higher level of leadership commitment due to greater involvement with the quality system and a more significant number of internal auditors as opposed to micro and small business organizations. In business organizations, leadership is satisfied with the quality management system and believes that the quality system has an impact on their business. The conducted research has also provided answers to the other goals set in dissertation.