This study investigated the impact of English Language proficiency testing on the pronunciation performance of undergraduates in South-west. Nigeria. The study was a descriptive survey research design. The target population size was 1243 (200-level) undergraduates drawn from eight tertiary institutions. The instruments used for data collection were the English Language Proficiency Test and Pronunciation Test. The English Language proficiency test was used to measure the performance of students in English Language and was adopted from the Post-UTME past questions from Babcock University Admissions Office on Post Unified Tertiary Admissions and Matriculation Examinations screening exercise (Post-UTME) for undergraduates in English and Linguistics. The test contains 20 objective English questions with optional answers. The instruments were validated through experts' advice as the items in the instrument are considered appropriate in terms of subject content and instructional objectives while Cronbach alpha technique was used to estimate the reliability coefficient of the English Proficiency test, a value of 0.883 was obtained. The research questions were answered with mean and standard deviation while hypothesis was tested with Pearson Product Moment Correlation Coefficient at 0.05 alpha level. The findings of the study revealed that the mean value of the students' English Proficiency and pronunciation scores were 66.36 and 74.21% respectively, which showed that the students' English proficiency and pronunciation performance were above average and high result respectively; there was a significant positive relationship between proficiency in English Language and pronunciation performance of the students who participated in the study (r = 0.589; p < 0.05).