This book constitutes the proceedings of the 20th Brazilian Symposium on Artificial Intelligence, SBIA 2010, held in S o Bernardo do Campo, Brazil, in October 2010. The 31 papers presented were carefully reviewed and selected from 91 submissions. The topics covered are: ontologies, knowledge representation and reasoning; machine learning; autonomous agents and multiagent systems; natural language processing; planning and scheduling; constraints and search; and logics for AI.