Many IELTS candidates cannot reach their target scores. One major reason is a lack of vocabulary. Vocabulary is essential for understanding and communication. It supports all four skills: reading, writing, listening, and speaking. Without enough vocabulary, learners struggle to perform well in the exam. This study examines how limited vocabulary becomes a key barrier to IELTS success. It focuses on common problems faced by learners. These include difficulty understanding reading texts, weak idea development in writing, and problems with listening and speaking. The study is based on a review of relevant literature and general learner patterns. The findings show that poor vocabulary knowledge lowers overall performance. Many students fail to reach band 6 or higher because of this issue. Vocabulary also affects confidence and fluency. The study suggests that improving vocabulary can increase IELTS scores. Targeted vocabulary learning helps students understand better and express ideas more clearly. Key words: IELTS, Vocabulary Knowledge, Language Barriers, Reading, Writing, Listening, Speaking, English Proficiency.