This volume constitutes the refereed proceedings of the 13th Asian Conference on Intelligent Information and Database Systems, ACIIDS 2021, held in Phuket, Thailand, in April 2021. The total of 35 full papers accepted for publication in these proceedings were carefully reviewed and selected from 291 submissions. The papers are organized in the following topical sections: data mining and machine learning methods; advanced data mining techniques and applications; intelligent and contextual systems; natural language processing; network systems and applications; computational imaging and vision; decision support and control systems; data modelling and processing for Industry 4.0.