This book constitutes the proceedings of the 20th Brazilian Symposium on Artificial Intelligence, SBIA 2010, held in São 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.