Developing intercultural sensitivity in the current multicultural world is an essential, but challenging requirement. This necessity is significant in EFL classes where learners are expected to gain intercultural skills to communicate more efficiently in culturally diverse contexts. Grounded in Bennett's (Bennett, International Journal of Intercultural Relation 10:179-196, 1986a) developmental model of intercultural sensitivity, the present study probed the developmental patterns of intercultural sensitivity (ICS) in a group of Iranian EFL learners, and their attitudes toward an online community of practice (CoP) in which they took part. To these ends, 15 Iranian EFL university students (8 females and 7 males) at upper-intermediate and advanced levels of proficiency were engaged in an online CoP discussing intercultural matters with 4 foreign interlocutors (2 females and 2 males) of differing sociocultural backgrounds. The online discussions lasted for 8 weeks, and data were collected through learners' recorded online discussions and follow-up semi-structured interviews. The Analysis of the written discourse of participants' online discussions revealed that the Iranian EFL learners mainly made defensive arguments and tended to minimize cultural differences. However, by the end of the online classes, a moderate shift in the learners' perspectives from ethnocentric worldviews to more ethnorelative perspectives of accepting cultural differences was observed. Interview findings indicated that the majority of Iranian learners were interested in the online discussions and acknowledged the usefulness of engaging in an online CoP in advancing their intercultural sensitivity. Drawing on relevant literature, these findings are discussed and implications for language instructors, teacher educators and learners are suggested.