In a strategic alliance, collaboration success requires special considerations because the partners are independent of each other. Maturity models are one of the tools for monitoring this success. This research aims to design a new model to measure the maturity level of strategic alliances. This goal has been achieved by identifying the model's dimensions, defining the maturity levels, and finally designing the method of determining the maturity level. A list of maturity level measurement indicators was obtained by studying the literature, previous successful and unsuccessful experiences, and interviewing experts to achieve this goal. After that, we gathered the necessary indicators using the content validity ratio method. Then the maturity levels of strategic alliances were defined. By evaluating 31 examples of strategic alliances, fuzzy sets for each indicator and maturity level were formed. To determine the maturity levels, the indicators' weights were calculated by fuzzy data envelopment analysis. Since the desired model did not seek to calculate the efficiency, data envelopment analysis without explicit input was used. By implementing the data envelopment analysis model, the best possible combination for the weight of the indicators was obtained. The model's validity was evaluated and confirmed by comparing the results of the implementation of this model with the evaluation results of the alliance examples. Based on this, the designed model determined the maturity level by using the obtained weights for different indicators, and finally, by de-fuzzifying this set, it calculated the maturity level of the strategic alliance.