The importance of learner autonomy has been researched for at least two decades. However, it has been critiqued that most research mainly focused on theoretical explanations and was based on anecdotal evidence (Dalgarno and Lee in "Br J Educ Technol "41(1):10-32, 2010; Hew and Brush in "Educ Technol Res Dev" 55(3):223-252, 2007). Therefore, this study aims to explore how learner autonomy is influenced by new technologies (a 3D virtual learning platform: Build & Show, B&S) through a case study with a quasi-experimental design. 29 fifth graders participated in this study for 4 months. Research data include the questionnaire on students' autonomy, the four-month none-participant classroom observation, the feedback of participating students and teachers, and an analysis of videos created by the students. The findings include (1) a rich description of the process of students' creations in B&S and of the uses of B&S in English classes; and (2) an analysis of the students' self-assessment of learner autonomy supported with the qualitative data. Based on these results, the possible approaches to improving learner autonomy in a 3D virtual world have been discussed.