This article presents a comprehensive comparative analysis of the vowel systems in English and Uzbek, two languages belonging to distinct linguistic families with significantly different phonological structures and articulatory principles. The study investigates the phonemic inventories, articulatory classifications, acoustic features, and phonological functions of vowel sounds in both languages. Special attention is given to the contrastive elements such as vowel quantity, vowel quality, diphthongization, centralization, reduction, and the role of stress in shaping vowel realization. The English language is characterized by a complex and dynamic vowel system involving monophthongs, diphthongs, and triphthongs, whereas Uzbek possesses a more symmetrical and stable vowel inventory with relatively consistent articulatory properties and without vowel reduction in unstressed syllables. The analysis highlights significant differences that lead to common pronunciation challenges for Uzbek learners of English due to phonological transfer effects. The findings contribute to the fields of comparative phonetics, second-language acquisition, phonology, and practical language teaching methodology.