Twitter is becoming increasingly popular as a medium for language learning. This study explores self-directed learning via social interactions that use Twitter as an interactive learning environment. The participants in this study were thirty university students of Chinese as a foreign language at levels 1 and 2 of the "Hanyu Shuiping Kaoshi" (HSK). Prior to the Twitter activity they self-assessed their confidence on content topics and made plans to self-direct their learning for seven weeks. In addition, they all took part in a training session in which they were given written instructions on how to tweet in a group message-board setting. The data that were collected included students' responses to a motivation questionnaire before and after the Twitter activity (pre and post motivation), their tweets, their evaluation of the Twitter activity, and their learning achievement based on their scores in the final exam. The analysis of their tweets is related to the curriculum content and their Twitter (activity) plan. The results showed that the students created an interactive learning environment to practice their Chinese with their peers in active sentence constructions. Students' Twitter behavior and motivation for using Twitter to practice Chinese correlated significantly with their learning achievement. In addition, students became familiar with a range of choices to practice Chinese. However, half of them failed to follow the Twitter plan they had drawn up and only one-fifth of their tweets involved social interactions. Finally, barriers to and suggestions for future research on microblogging in the learning of Chinese are discussed.