Work objective includes the development of risk level estimation method for the implementation of the business processes reengineering projects at the instrument-making enterprises based on fussy set theory. The article analyzes and highlights the risks in the system of project management and reengineering programs for business processes at enterprises. The risk groups and their types that can arise during the reengineering of business processes at instrument-making enterprises are systematized and allocated, in particular: investment, financial, organizational, technical, technological, operational and informational. To assess the impact of these risks on the effectiveness of reengineering projects, a method based on the theory of fuzzy sets is proposed.