This study discusses the effects of using multimedia assisted instruction for Mandarin vocabulary learning by Vietnamese students with the assistance of the ASSURE model. The aim is to understand the difficulties encountered by these students and the effects during the learning progress of multimedia assisted instruction. In order to fulfill the above-mentioned study purposes, this study makes use of qualitative research methods such as interviews, participant observation, and document analysis to follow the progress of 11 Vietnamese students for three months. The study results showed that the use of multimedia assisted instruction could promote the learners' speed of understanding and memorization of vocabulary. Better transfer of learning during the simulation scenario was also shown. Moreover, the test results of most students showed significant improvement after using multimedia assisted instruction. However, some difficulties were encountered during the learning process, for example; too much English content in the multimedia teaching materials was not necessarily helpful. Students were also subject to loneliness because of the use of multimedia when practicing by themselves after class. This led to insufficient interaction with teachers and classmates. Students with weak initiative and will power would be influenced and distracted by other information from the Internet. (Contains 3 tables.)