This quasi-experimental research explored Chinese as a Foreign Language (CFL) learners' use of a popular social networking application in China, WeChat, in acquiring vocabulary. The research questions answered in this study are: (1) How may the CFL learners' vocabulary performance be described in terms of: (a) pretest scores and (b) posttest scores; (2) Is there a significant difference between the performance in pretest and posttest of the control group and experimental group?; (3) What are the implications of the results of this study in teaching? Participants joined the ten-day treatment wherein they used the three features of WeChat: WeChat Messaging, Official Accounts, and Mini Programs. The participants' performance before and after the treatment were identified using pretest and posttest. In addition, observation checklists were utilized to determine the change in behavior in acquiring vocabulary of the CFL learners. Results suggested that WeChat could improve students' vocabulary acquisition in foreign language. Suggestions for improvements in future WeChat treatment were also discussed.