The purpose of this study is to explore the influence on the learning effectiveness for mental retardation students by using the agent-based word-recognition learning system. The system applied the teaching agent to increase learner's motivation and used stimulus fading strategy to enhance the learning effectiveness. A multiple probes of single-subject design was adopted. A nine-year-old pupil with moderate mental retardation participated in the study. The experiment shows that the subject can identify the target words correctly without the presence of known pictorial cues. The learning system combining teaching agent and stimulus-fading strategy is efficient in teaching word recognition for pupils with moderate retardation.