This study aims to investigate the effects of answering given questions and self-question generation on the understanding of main ideas of an expository text. 58 Chinese learners who had studied Japanese for about 1 and a half years in Japanese-language schools in Japan were assigned to one of 3 groups: question answering (QA), question-generation (QG), and read-reread control group. Each group was given the same piece of text to read. The QA group had to answer given questions and the QG group generated their own questions and answers about the main ideas of the text whilst they read. Each group was then given a free recall task and then was given back the text and was asked to circle the main ideas. The results showed that there was no difference in the amount of recall between the 3 groups in the free recall task. However, only the QG group recalled more main ideas than details. The QA and Control groups recalled a similar percentage of main ideas, and that in the later task both the QG group and Control group selected sentences that referred to main ideas. However, the QA group selected sentences that related to the previously given questions, irrespective of main ideas or details. The findings showed that selfquestioning had positively affected the ability to recall main ideas. However, it didn't affect the ability to select main ideas. The results supported previous research that found that the question answering groups' mental process focuses the learner's attention point around the answers to the given questions. These findings implied that self-question generation aids the understanding and memory of the main ideas of an expository text.