The Patani Malay dialect is one of the Malay dialects spoken in southern Thailand, primarily in Pattani, Yala, Narathiwat, and parts of Songkhla. Based on several studies on the Patani Malay dialect that have previously discussed, it can be confirmed that no researcher has yet attempted to reconstruct the proto form of the Patani Malay dialect, especially in the Narathiwat region. Accordingly, this study aims to reconstruct a proto-dialect known as the Proto-Patani Malay dialect of Narathiwat (PPMDN), with a focus on two main components: vowels and diphthongs. Vowel and diphthong reconstruction is selected because these two sound types form the foundation of historical linguistic research. The approach used in this study is a descriptive qualitative method based on a historical linguistic approach. This research employs two central methods to gather linguistic information and data: library research and field research. The study focuses on several villages in the Narathiwat region, including Kresor (KRS), Buketa (BKT), Puyok (PYK), Munok (MNK), Benae Luwas (BNL), and Aikubu (AKB). The analysis conducted shows that the PPMDN has eight vowel phonemes, namely the vowels *i, *u, *e, *ɘ, *o, *ɛ, *ɔ, and *a, which consist of two vowels narrow, three semi-narrow vowels, two semi-wide vowels, and one broad vowel and has five diphthong phonemes, namely diphthongs *ai, *ae, *aɛ, *au, and *ao. This study is expected to contribute to and further develop knowledge in Malay linguistics, particularly concerning the Patani Malay dialect.