The study aims to identify an inventory of vowel phonemes of Melanau Rajang dialect in Belawai under the administration of Tanjung Manis District, Sarawak. This study is a field survey using interview methods to obtain data. A total 250 Swadesh list (Samarin, 1967) are used as a guide for data collection. In this study, two infotmants of different genders aged between 40 and 60 years old were selected based on criteria of informant selections according to Asmah Haji Omar (2001). In analysis data, qualitative method is used based on structural approaches. The findings show that there are eight (8) vowel phonemes have been identified; four (4) front vowels [i, e, ε, a]; one (1) central vowel [É™]; and three (3) back vowels [u, o, É”]. Besides that, the distribution/alternation of all vowel phonemes of Melanau Rajang dialect in Belawai are also discussed in this study. The findings also indicate that active vowel phonemes are vowels [a, i, u], while inactive vocal phonemes are vowels [É”, o, ε, É™, e].