<p>The evolution of retail platforms and online marketplaces fundamentally transformed consumer expectations from their product purchases, particularly the last-mile delivery (LMD). In this era of urbanization, companies also strive for Sustainable Last Mile Delivery (S-LMD). Attaining the S-LMD has become challenging amid the environment concerns in online retailing. However, there are many obstacles in the way of attaining S-LMD, especially in a nation as diverse and dynamic as India. By thoroughly examining the challenges impeding the adoption of S-LMD in India's online retail industry, this study systematically identified, examined, and ranked the particular barriers of sustainable LMD. For ranking the S-LMD obstacles, we have applied Spherical Fuzzy Analytic Hierarchy Process (SF-AHP) technique. The SF-AHP has been a new tool that has been used for the very first time for identification and analysis of S-LMD related barriers. The extracted barriers were assessed by experts. Data was gathered with the help of expert interviews by academicians and business professionals throughout India. Five key categories of barriers were found by the study, which were then further categorised into 21 sub-barriers. After considering the global weights related to the full set of sub barriers it was found that Limited Sustainable Infrastructure, Traffic congestions and population density, High Initial Investment Cost for adopting S-LMD measures, Lack of Technical Knowledge on sustainable practices and infrastructure and Pressure for lower prices holds the top 5 positions among all the 21 sub-barriers which work as impediment for S-LMD. This study significantly contributes to the sustainable supply chain sector by bringing out the tactical recommendations and practical insights. Policymakers, logistics firms, and online corporations trying to build successful interventions for S-LMD in India and other emerging countries will find it to be a constructive resource.</p>