Recent innovations in autonomous driving have spotlighted its potential in last-mile delivery, but there is insufficient research to understand consumers’ acceptance of autonomous delivery service (ADS) powered by autonomous driving technology. We fill this research gap by examining the role of technology readiness (TR) in influencing consumer acceptance of ADS in an extended Behavioral Reasoning Theory framework. We find that two TR traits, namely innovativeness and discomfort, can affect both individuals’ reasons for and against accepting ADS. However, optimism and insecurity, as two other TR traits, only influence the positive and negative reasoning for accepting ADS respectively. The influences of TR traits on consumers’ acceptance intention are mediated by the reasoning process, where the “reasons for” demonstrates stronger effect than “reasons against”. Our study also investigates the antecedents of TR traits, with the findings that younger individuals have both stronger TR motivators and weaker TR inhibitors while better educated consumers only demonstrate stronger TR motivators. This study offers valuable insights into the innovation acceptance in last-mile delivery service, with theoretical and managerial implications.