This study investigated the effect of task choice and self-efficacy on task interests with 7th graders. They were given a set of ill-defined problems and asked to propose the solutions. In experiment 1, the types of choice (choice/assignment) and task difficulty (difficult/easy) were manipulated in small group collaborative learning situation. The result showed that there were significant two-way interaction effects on task interests between self-efficacy and choice, and between self-efficacy and the task difficulty. This finding indicated that participants with low self-efficacy were more interested in choice condition and easy task condition, whereas participants with high self-efficacy were more interested only in the difficult task. In experiment 2, the types of choice and levels of competition (high/low) were manipulated in individual learning situation. The results revealed a significant three-way interaction, indicating that participants with high self-efficacy showed more interests in choice condition when they were in highly competitive situation, whereas participants with low self-efficacy showed more interests in choice condition when they were less competitive situation. These findings suggest that it is desirable for highly efficacious students in a small group activity to provide a difficult task and for less efficacious students to provide an easy task and task choice. In contrast, in individual learning situation, it is recommended that it is beneficial to provide task choice for the students with high self-efficacy only in a competitive learning environment and for those with low self-efficacy to provide task choice only in a less competitive learning environment.