This research investigated the effects of online immediate feedback on the reading comprehension of 56 Iranian female learners, randomly assigned to experimental (receiving online immediate feedback) and control (receiving teacher-immediate feedback) groups. The study was performed through a quasi-experimental pretest–posttest control group design, using the Oxford Quick Placement Test (OQPT) proficiency examination and a semi-structured questionnaire as research tools and Read Theory as the online platform. Statistical analysis revealed that the groups were initially equivalent, and the posttest results revealed considerable improvements in the experimental group’s performance, with a large effect size (d=2.31). As expressed by the participants in this group, online feedback made the errors clearer, reduced anxiety, and increased motivation (M=3.94 for comprehension and 3.89 for motivation). Qualitative investigations revealed that feedback was an effective tool helping learners notice and correct their mistakes, and consequently deal with the challenging reading material. The control group reported positive evaluations of teacher feedback, appreciating the clarity, individualized approach, and motivating effects of teacher feedback, although limited time and unequal attention were reported as some drawbacks. The findings highlight the significant contribution of both online and teacher feedback to comprehension and motivation enhancement. However, the generalizability of the results may be influenced by several limitations, including technical problems, classroom environment, and participant homogeneity.