Due to recent pandemic, 2021 International Conference on Internet of Things and Smart City (IoTSC2021) was held virtually online on June 4, 2021. The decision to hold the virtual conference was made in compliance with many restrictions and regulations that were imposed by countries around the globe. Such restrictions were made to minimize the risk of people contracting or spreading the COVID-19 through physical contact. There were 45 individuals who attended this on-line conference, represented many countries.IoTSC 2021 aims to bring together innovative academics and industrial experts in IoT and Smart City to a common forum. The primary goal of the conference is to promote research and developmental activities in IoT and Smart City and another goal is to promote scientific information interchange between researchers, developers, engineers, students, and practitioners working all around the world. Every year, the conference will be held to make it an ideal platform for people to share views and experiences in IoT and Smart City, and related areas.During the conference, the conference model was divided into three sessions, including oral presentations, keynote speeches, and online Q&A discussion. In the first part, some scholars, whose submissions were selected as the excellent papers, were given about 5-10 minutes to perform their oral presentations one by one. Then in the second part, keynote speakers were each allocated 30-45 minutes to hold their speeches. In the second part, we invited three professors as our keynote speakers. Prof. Juan M. Corchado, from Department of Computer Science, University of Salamanca, Spain. He is the President of the IEEE Systems, Man and Cybernetics Spanish Chapter and the Academic Director of the Institute of Digital Art and Animation, University of Salamanca, where he is currently a Full Professor. The second keynote speakers, Prof. Xiaojun Wu, from Jiangnan University, China. Lastly, we were glad to invite Prof. Fabien Ferrero, from Université Cote d’Azur, France as our finale keynote speakers. His studies concerned design and measurement of millimetric antennas, IoT systems and reconfigurable antennas. Their insightful speeches had triggered heated discussion in the third session of the conference. Every participant praised this conference for disseminating useful and insightful knowledge.The proceedings are a compilation of the accepted papers and represent an interesting outcome of the conference. Topics include but are not limited to the following areas: Data Security and Privacy Protection, IoT Big Data Storage and Mining, IoT Applications, Internet Technology, Soft Computing and Intelligent System and other related topics. All the papers have been through rigorous review and process to meet the requirements of international publication standard.We would like to acknowledge all of those who supported IoTSC2021. The help and contribution of each individual and institution was instrumental in the success of the conference. In particular, we would like to thank the organizing committee for its valuable inputs in shaping the conference program and reviewing the submitted papers.We sincerely hope that the IoTSC2021 turned out to be a forum for excellent discussions that enabled new ideas to come about, promoting collaborative research. We are sure that the proceedings will serve as an important research source of references and knowledge, which will lead to not only scientific and engineering findings but also new products and technologies.Committee of IoTSC2021List of Committee member, are available in the pdf