<p>Faecal sludge (FS) from on-site sanitation systems, characterized by high organic matter and pathogen loads, poses substantial public health and environmental risks if not adequately treated. The selection of FS treatment technologies for decentralized sanitation systems in low- and middle-income countries remains challenging due to data uncertainty, competing sustainability objectives, and the need to address multiple treatment stages. This study proposes a fuzzy logic-based decision-making framework for resource-limited settings to evaluate and rank the sustainability of FS treatment technologies across three stages: dewatering, leachate treatment, and sludge stabilisation. Technical, socio-economic, and environmental criteria and sub-criteria were identified through literature review and experimental data. Fuzzy inference systems (FIS) were developed using prioritized rules that precede the factors to reflect the relative importance of the critical criteria. The framework generated individual technical, socio-economic and environmental scores, which were aggregated into overall sustainability scores. Among dewatering treatment technologies, drying beds achieved the highest sustainability score of 78.7, while the constructed wetland achieved the highest sustainability score among FS leachate treatment technologies with 71.3. In the dried FS stabilization options, Co-composting ranked first, with a score of 39.4. These high-performing technologies are largely based on Nature-based Solutions (NbS), which utilize natural processes for waste treatment. The findings highlight the potential of NbS within an integrated faecal sludge management system, demonstrating their suitability for decentralized sanitation in resource-limited settings due to their low energy demand, ecological compatibility, and sustainability. Rankings remained consistent across all FIS methods, confirming the stability of the sustainability evaluation framework.</p>