This quasi-experimental study investigates the effects of collaborative activities on tertiary-level EFL students' learner autonomy in Turkey. To achieve this aim, both quantitative and qualitative data were collected with the help of a learner autonomy questionnaire, index cards filled out by the students, the instructor's journal, and an interview with the instructor of the experimental group. Two groups of 40 students in total from the preparatory program of a central Anatolian university were appointed as experimental and control groups. The results of the quantitative data analysis revealed that, after the implementation of collaborative activities in three consecutive weeks, there was a statistically significant difference between the groups in terms of their autonomy level; the students in the experimental group scored higher than those in the control group, which implies that they showed more autonomous skills in areas such as motivation, curiosity to learn, risk-taking, problem solving and decision making skills to improve learning. The results of the qualitative data analysis revealed that collaborative activities employed in this study (e.g., problem-solving activity, role-play, games) allowed participants to learn from each other, and gain a sense of responsibility. The overall results suggested that collaborative learning practices could be implemented to help EFL students increase their learner autonomy level. Additionally, curriculum and assessment methods of educational institutions might be revised to include more collaborative activities.