This empirical study attempted to investigate the effect of using online communities of practice in teacher education on pre-service teachers' critical thinking dispositions. California Critical Thinking Disposition Inventory and the comments posted to the online community of practice were used as the data collection tools. Results showed that online communities of practice did not affect pre-service teachers' overall critical thinking disposition significantly. However, research results revealed that the scores that pre-service teachers have achieved from self-confidence and open-mindedness sub-factors of the inventory have significantly differentiated in favor of the pre-service teachers in the experimental group. The statements that pre-service teachers have made on their comments were weak in terms of critical thinking. Pre-service teachers have mostly expressed their own views and they have usually supported each other by providing positive opinions. Therefore, it is thought that online communities of practice affect positively only pre-service teachers' self-confidence tendency and the abilities to express their own opinions.