Introduction. The authors’ method of the objective evaluation of the maturity level of the organization for obtaining sustainable success on the basis of self-assessment is described. The technique is based on the use of expert information and mathematical apparatus of the fuzzy sets theory. The substantiation of the chosen approach is presented. It allows promptly analyze the organization state and apply full expert information. It is proposed to use expert assessments of maturity levels for each of the activities according to GOST R ISO 9004-2010. A brief description of the fuzzification stages content, composition and defuzzification which are the essence of the fuzzy modeling process to obtain reliable estimates is given. Materials and Methods . As follows from the analysis, a generalized model of the “evaluation of the maturity level of the organization” domain is developed. The input and output linguistic variables corresponding to the maturity main criteria in accordance with GOST R ISO 9004-2010 are simulated; and the base term sets are defined. Membership functions of all the linguistic variables are developed according to the estimates of four experts for which purpose the typical trapezoidal functions are used. An expanded form of the fuzzy logic inference for the considered system of knowledge is presented. Taking into account the calculated significance coefficients of the basic maturity criteria, a knowledge base is created. It includes 729 production rules and serves as a basis for the logical deduction of the evaluation of the organization maturity level. Research Results. The barycenter method is used to calculate the precise value of the maturity level. It is implemented in Matlab with the help of Fuzzy Logic Toolbox application package. Response surfaces showing the relationship of the linguistic variables are constructed. The fuzzy inference of the evaluation of the organization maturity level using the proposed techniques is exemplified. Discussion and Conclusions. The presented methodology using a mathematical apparatus of the fuzzy sets theory allows an objective estimation of the organization maturity level for sustained success. It is designed for prompt analysis of the organization on the basis of the self-assessment performed by experts.