This book constitutes the refereed proceedings of the Third International Conference on Smart Blockchain, SmartBlock 2020, held in Zhengzhou, China, in October 2020. Due to COVID-19 pandemic the conference was held virtually. The 39 papers presented in this volume were carefully reviewed and selected from 139 submissions. They focus on a broad range of topics in the area of blockchain, from privacy-preserving solutions to designing advanced blockchain mechanism, from empirical studies to practical manuals.