This study investigates preservice teachers' trust levels and collaborative communication behaviors namely leadership, feedback, social interaction, enthusiasm, task and technical uncertainties, and task-oriented interactions in online learning environment. A case study design involving qualitative and quantitative data collection and analysis was employed. The sample consisted of 32 (24 female, 8 male) 3rd year foreign language education students who enrolled in the "Instructional Technology and Material Development" course at Middle East Technical University in Ankara, Turkey. The participants were involved in a four-month online project in the "Learning to Teach with Technology Studio" (LTTS) course at Indiana University in the US to create a technology supported project-based learning unit for foreign language learners. At the end of the fourteen-week period, the participants filled out the online Group Trust Questionnaire consisting eight five-point Likert-type items and two open-ended questions. To identify the participants' online interactions, online discussion archives of the groups were analyzed. The findings showed that the groups with different trust levels showed different communication behaviors throughout the study, and midpoint of the group life was found critical moment for increasing or decreasing pattern of communication behaviors. (Contains 8 tables and 1 figure.)