Task-based instruction (TBI) is a pedagogical approach that centers on engaging learners in meaningful and communicative tasks to promote language acquisition, active participation, and practical language use. The primary objective of this investigation was to assess the influence of TBI on reading comprehension, motivation for L2 reading, anxiety, and L2 grit. Thus, two pre-existing classes from a large university in China were selected and one of them was assigned as the treatment and the other as the comparison group. An Oxford Quick Placement Test determined that the subjects possessed an intermediate level of proficiency. The experimental group received reading comprehension-based TBI, while the control group received traditional lecture-based strategy training. Each of the dependent variables was tested at two points of time. Based on a conducted t-test, while both groups knew exactly the same as time 1, the comparison group did less on the posttest in terms of reading comprehension skills than its treatment counterpart. The effect size was large. Furthermore, the results of a series of chi-squares showed that TBI had facilitating effects on motivation for L2 reading, language learning anxiety, and L2 grit, all with large effect sizes. That is, on the posttest, the number of motivated learners and grittier learners in the treatment group increased, while the number of high-anxiety learners in the experimental group decreased sharply. However, the participants’ motivation for L2 reading, anxiety, and L2 grit did not significantly change after the treatment. The implications of the study are explained.