PDAs (Personal Digital Assistants) have been used widely in educational settings. In this study, the visual illustration of a scientific text (cognitive-interest illustration, emotional-interest illustration, or no illustration) was manipulated to investigate its impact on student interest in instructional materials, achievement, and time spent on reading materials in PDA-based learning. Forty-five graduate students were randomly assigned to one of the three treatment groups: the cognitive-interest illustration group, emotional-interest illustration group, and the text only group. Each group was given instructional material corresponding to the treatments. Results revealed that the levels of post-interest across the groups were not significantly different among the three groups. However, the students in the cognitive-interest illustration group showed significantly higher achievement than those in the emotional illustration group and the text only group. Implications of the findings as a catalyst for further research in the development of instructional materials for PDA-based learning were discussed.