One of the fundamental challenges in municipal waste management is ensuring the long-term stability of landfills. Slope instability in these structures can lead to irreparable consequences, including environmental pollution, infrastructure destruction, and public health threats. Therefore, accurate assessment and prediction of slope behavior in these structures is of particular importance. In this study, a new method based on fuzzy logic has been proposed to assess and predict slope stability in landfills. Fuzzy logic, as a powerful tool in modeling complex and uncertain systems, allows for more accurate analysis of landfill behavior. In order to conduct the present study, various steps were taken, including data collection, modeling with fuzzy logic, determining model coefficients, and model validation. In the first step, field data were collected from various excavations such as slope geometry, soil mechanical properties, groundwater level, loading due to waste, etc. Then, a fuzzy logic model was developed to analyze slope stability. In this model, input parameters such as slope, elevation, soil type, and groundwater level were described as linguistic variables and converted into fuzzy numbers using membership functions, and finally, fuzzy rules were defined to express the relationships between inputs and output (slope stability or instability). In the next step, field and laboratory data were used to determine the coefficients of the fuzzy model, and using optimization methods, the model parameters were adjusted in such a way that the model output was consistent with the observed data. In the last step, the developed model was validated using new data. For this purpose, the model results were compared with the observed data and the accuracy and reliability of the model were evaluated. The results show that the developed model will be able to predict the probability of slope instability with high accuracy and identify areas with high risk of instability in landfills. Also, it was determined that by analyzing the sensitivity of the model, important factors that affect slope stability can be identified. According to the model results, appropriate solutions can be provided to improve slope stability, such as changing the slope angle, soil reinforcement, and drainage. As a general conclusion, based on the observations of the present study, it can be said that using fuzzy logic in analyzing the slope stability of landfills is a new and efficient approach that can significantly contribute to improving urban waste management and reducing risks from slope instability.