This book constitutes refereed proceedings of the 5th International Conference on Data Mining and Big Data, DMBD 2020, held in July 2020. Due to the COVID-19 pandemic the conference was held in a fully virtual format. The 7 full papers and 3 short papers presented in this volume were carefully reviewed and selected from 39 submissions. The papers present the latest research on advantages in theories, technologies, and applications in data mining and big data. The volume covers many aspects of data mining and big data as well as intelligent computing methods applied to all fields of computer science, machine learning, data mining and knowledge discovery, data science, etc.