<![CDATA[Vocabulary mastery is an essential component of English language learning because sufficient lexical knowledge enables students to understand language input and express ideas effectively. However, tenth-grade students at State Senior High School 2 Tondano still experience difficulties in understanding, remembering, and using English vocabulary, particularly nouns. This study aimed to determine whether the use of animated YouTube videos could improve the noun vocabulary mastery of tenth-grade students at State Senior High School 2 Tondano. A quantitative approach with a pre-experimental one-group pre-test and post-test design was employed. The participants consisted of 25 tenth-grade students. Data were collected using a 25-item vocabulary test administered before and after the treatment. The treatment involved the use of animated YouTube videos as instructional media for vocabulary learning. The data were analyzed using descriptive statistics, the Shapiro–Wilk normality test, and a paired-samples t-test through SPSS. The findings revealed a clear improvement in students’ vocabulary scores after the treatment. The mean score increased from 45.44 in the pre-test to 71.36 in the post-test, representing a mean gain of 25.92 points. The minimum score increased from 32 to 56, while the maximum score increased from 60 to 88. The paired-samples t-test also indicated a statistically significant difference between the pre-test and post-test scores (p<.05). These findings suggest that animated YouTube videos can provide meaningful visual and auditory input that supports students’ understanding and retention of target vocabulary. Therefore, animated YouTube videos can be considered an effective and engaging instructional medium for improving noun vocabulary mastery among Indonesian EFL learners.]]>
