Peer feedback has been shown to be an effective strategy to improve academic achievement. However, little evidence is available about the effects of peer feedback on academic outcomes other than achievement, such as academic self-concept (ASC). ASC and achievement are reciprocally related and thus mutual reinforce themselves. The present study focuses on the effect of a four week long structured web-based peer feedback intervention on ASC in the domain of academic writing as a part of a seminar assignment in a sample of undergraduate psychology students. The study investigated the effectiveness with 49 students in a randomized-controlled trial with a pre-and post-test. Each student acted as an author and a reviewer. Results indicated significant improvements in ASC for the domain of academic writing over time as compared to a control group. Furthermore, the causal effect of peer feedback compared to no feedback on ASC for academic writing was strong with d = 0.72. The effect was domain specific, as the ASCs for the sub-domains statistics and language remained unchanged by the intervention. Overall, the results revealed that participation in a peer feedback system is an effective method to enhance ASC in the context of higher education.