Researchers conducted this research because all teachers and students need several applications to facilitate teaching and learning activities. Therefore, the researcher implemented the U-Dictionary application to solve student problems. This thesis aims to determine the improvement of students vocabulary mastery in English using the U-Dictionary application. The subjects of this study were seventh-grade students at MTsN 5 Kediri. The researcher used classroom action research to conduct this research. The research instrument was a test sheet and an observation sheet. This research was conducted in two cycles. The researchers procedure in this study consisted of four steps. They are planning, acting, observing, and reflecting. The success criterion is 75%. Researchers conducted this research offline. So, all activities such as preliminary test, cycle test-1, and cycle test 2 were directly carried out with students in the classroom. From the findings and discussion, it is found that the U-Dictionary application can improve students vocabulary mastery in English. This can be seen in test cycle 2. In cycle 1, the student scores showed that there were 25 students who passed and 17 students who failed. The average test score in cycle 1 was 73.71 while the percentage of students who succeeded was 59.52%. While the results of the observation sheet show the percentage of student activity is 70%. From the results of the analysis of the data collected in cycle 1, this research needs to be continued in the next cycle with several improvements to the learning scenario. In cycle 2, the student scores showed that 34 students passed and 8 students failed. The average test score in cycle 2 was 86.80 and the percentage of students who succeeded was 80.95%. While the results of the observation sheet in cycle 2 showed the percentage of student activity was 83.33%. This shows that in cycle 2 the students scores have met the success criteria of 75%. Thus, based on the results of cycle 2, the U-Dictionary application can improve students vocabulary mastery in English

Wasiani , Nur .   (2022). Using U-Dictionary To Improve Students English Vocabulary Mastery In Descriptive Text At Mtsn 5 Kediri. IAIN Kediri