This study investigated the relationship between changes in language learning beliefs and English proficiency among 41 Korean university students who participated in a short-term English program. Participants' beliefs were assessed using the Beliefs About Language Learning Inventory (BALLI), and their proficiency was measured using the Test of English for International Communication (TOEIC). Frequency analysis, descriptive statistics, paired-sample t-tests, and correlation analysis were employed to analyze the data. The study found significant improvements in both listening and reading scores, and changes in beliefs varied with proficiency gains. Students with higher proficiency gains demonstrated improved confidence and self-efficacy, and decreased instrumental motivation, whereas those with lower gains exhibited minimal changes in beliefs. Correlation analysis revealed that belief shifts, such as reduced self-consciousness and increased integrative motivation, were positively related to proficiency gains. These findings suggest the dynamic nature of learners' beliefs and their potential impact on language learning outcomes, highlighting the importance of addressing belief systems in English language education.