Nursing professionals who aim to work as registered nurses (RN) in English speaking countries are required to pass two kinds of test: an English standardized test such as IELTS/ TOEFL/TOEIC, and a test that assesses their nursing knowledge, namely the National Council Licensing Examination for Registered Nurses (NCLEX RN exam). The present study investigates whether or not employing an NCLEX RN mobile learning app called 'NCLEX RN Mastery 2015' can help improve nursing students' medical terminology knowledge. Students' overall perception of the app in terms of attractiveness and usefulness was also investigated as a part of qualitative analysis in this study. Participants were 51 nursing major students from a University of Science and Technology located in Northern Taiwan, enrolled in a five-week RN vocabulary intensive course. A pretest, 3 quizzes, and a posttest were administered to assess participants' vocabulary knowledge before, during, and after the use of the NCLEX RN Mastery 2015 mobile app, respectively. At the end of the course, participants were given questionnaires about their perceptions of the mobile app. The results suggested that, although the improvement in the posttest could not be entirely attributed to the use of the mobile app, students with high motivation to take the RN test considered the mobile app appealing and useful in their vocabulary learning. In addition, they were willing to purchase the full version of the mobile app. We also discussed pedagogical implications and directions for improvement of nursing English mobile learning apps to better suit the learning situation in Taiwan.