This study aims to investigate the effects of an inferential question discussion program on inferential comprehension and reading comprehension of fourth grade students. A quasi-experimental design was adopted. The participants were 71 fourth graders selected from two classes of an elementary school in Keelung County. There were 36 students in the experimental group and 35 students in the control group. The experimental group was treated with the inferential question discussion program, while the control group did not receive any experimental treatment. The results showed that the inferential question discussion program significantly improved students’ inferential comprehension performance on takes of referential, elaborative, and analogical inference in the Inferential Comprehension Test. Regarding the spontaneous inferences, the training program significantly increased the quantity and quality of students’ spontaneous inferences on the aspects of referential inference and summarization. The training program also effectively improved students’ reading comprehension performance. Instructional application and future research were discussed.