Purpose. Construction of an economic and mathematical model of the optimal organization of a system of business processes and its testing at an enterprise in the field of engineering services. Methodology. Methods of analysis and synthesis, systematization, theoretical generalization are used to study approaches to optimizing business processes of enterprises; modeling to create an economic and mathematical model of the optimal organization of the system of business processes; approbation of the developed model at an enterprise in the field of engineering services. Findings. The article proves the need to assess the impact of various economic factors on the financial results of economic activities of enterprises and the construction of business systems of enterprises, economic and mathematical models for their optimization. It has been determined that business process modeling is an effective means of improving quality management systems in accordance with the requirements of the international standard ISO 9001:2015, determining, identifying and minimizing the risks of enterprises, ensuring their successful activities in general. An economic and mathematical model has been developed for the optimal organization of the system of business processes of an enterprise as a means of maximizing the total profit from the implementation of works and services. Originality. An economic and mathematical model of the optimal organization of the system of business processes of enterprises in the field of engineering services has been built as an effective tool for improving their quality management systems and activities in general. Practical value. The use of the constructed economic and mathematical model of the optimal organization of the system of business processes of enterprises in the field of engineering services will provide the management team with important information for making management decisions aimed at improving quality management systems, achieving key business goals and maximizing profits.