This book constitutes the refereed proceedings of the 20th International Symposium on Knowledge and Systems Sciences, KSS 2019, held in Da Nang, Vietnam, in November 2019.The 14 revised full papers presented were carefully reviewed and selected from 31 submissions. This year KSS provides opportunities for presenting interesting new research results, facilitating interdisciplinary discussions, and leading to knowledge transfer under the theme of "Knowledge Science in the Age of Big Data".