Reading is one of the four essential English language skills, playing a crucial role in vocabulary acquisition and overall language proficiency. However, many students struggle with reading, particularly in comprehending texts and acquiring new vocabulary, which hinders their ability to communicate effectively. To address this challenge, extensive reading is considered an effective strategy, as it exposes students to a wide range of vocabulary in meaningful contexts. In response to this issue, the researcher conducted this study to explore how this approach can enhance students' vocabulary mastery. In this research, the main problem is “Is there any significant impact of extensive reading on vocabulary acquisition among students at SMK Muhammadiyah Jember?” and the objective is “to analyze the effect of extensive reading on students’ vocabulary acquisition.” Based on the research problem and relevant theories, the hypotheses are formulated as follows: null hypothesis (H₀): There is no significant impact of extensive reading on vocabulary acquisition, and alternative hypothesis (Hₐ): There is a significant impact of extensive reading on vocabulary acquisition. This study employs a quantitative method with a quasi-experimental design. The sample consists of grade XI students at SMK Muhammadiyah Jember. Data were collected through pre-tests and post-tests measuring vocabulary acquisition, focusing on nouns, verbs, adjectives, adverbs, and pronouns. The research instrument included a vocabulary test validated for content and reliability. The results demonstrate a statistically significant difference (Asymp. Sig. = 0.000 < 0.05) between the experimental and control groups, with the experimental group showing substantially higher vocabulary acquisition (mean rank 23.47 vs 9.53), confirming that extensive reading effectively enhances vocabulary learning while also fostering motivation, engagement, and independent learning habits, leading to the conclusion that integrating extensive reading into the curriculum would significantly improve students' vocabulary acquisition and overall language proficiency while cultivating a lasting reading habit.