This study explores whether and how peer pressure influenced students' participation in web-based peer learning (WPL). Fifteen students enrolled in a university reading course were followed over the course of one semester, and interviews with them along with the researcher's observational notes on their learning activities were qualitatively analyzed. Peer pressure slowly and steadily occurred during the students' WPL, with the students feeling differently about it at different levels. All of the students became somewhat used to it later in the semester. The peer pressure was mainly influenced by technological factors (e.g., the openness of the web platform) and non-technological factors (e.g., the academic gaps between students), along with other accompanying reasons (e.g., self-motivation for looking academically decent). The study concludes that students' experiences of peer pressure in relation to WPL involved a gradual process, had multiple causes, and ultimately positively impacted the students, although in the process, peer pressure exerted either negative or positive power on the students.