This book constitutes the refereed proceedings of the 9th Pacific Rim International Conference on Artificial Intelligence, PRICAI 2006, held in Guilin, China in August 2006. The 81 revised full papers and 87 revised short papers presented together with 3 keynote talks were carefully reviewed and selected from 596 submissions. The papers are organized in topical sections on intelligent agents, automated reasoning, machine learning and data mining, natural language processing and speech recognition, computer vision, perception and animation, evolutionary computing, industrial applications, intelligent agents, automated reasoning, evolutionary computing, game, machine learning and data mining, information retrieval, natural language processing, neural networks, and computer vision.