<p>Peer feedback, being an essential component of the learning process, was relatively ignored in terms of its connection to speaking skills, despite a vast amount of research on specifically peer feedback and feedback in general, particularly in writing. In this sense, this study aimed to examine the effect of written peer feedback on learners’ speaking performance and find out the feedback types preferred by students when providing online written peer feedback. It also sought to explore the perceptions of learners regarding online peer feedback exchange. This study followed a mixed-method approach, combining both quantitative data obtained through pre- and post-speaking tests and qualitative data through online written feedback of learners and semi-structured interviews. Twenty-nine tertiary-level students who were enrolled in a listening and speaking course participated in the study. The participants were given assignments to prepare four video presentations collaboratively as out-of-class tasks and then were asked to receive and give online written peer feedback after each video presentation in class over an academic term. Content analysis was conducted to analyze the qualitative data, and a paired samples t-test was carried out to reveal whether the speaking post-test results significantly differed from their speaking pre-test results. The results demonstrated that peer feedback significantly improved the overall speaking performance of learners, as well as their fluency, vocabulary, and pronunciation. Moreover, the participants developed positive attitudes towards peer feedback regarding pronunciation and motivation, and the expressive-approval feedback was determined to be the most preferred type for providing online written peer feedback. In conclusion, online peer feedback had both academic and affective benefits, and it should be integrated into the speaking classes considering the feedback perceptions and preferences of learners.</p>