The literature describes the Alasha dialect of Mongolian, which was originally an Oirat language, as having partially lost its Oirat features (in a ‘de-Oiratization’) and evolved into an interlanguage due to the interference of Inner Mongolian dialects. However, no study has performed a detailed examination of the influence of Inner Mongolian dialects and the realization of de-Oiratization. To address this research gap, this study focuses on the velar obstruent K in the Alasha dialect, which date back to *k in Proto- Mongolian, and analyses their phonetic realization using survey data. In Oirat Mongolian, the sound that dates backs to *k in Proto-Mongolian is realized as the plosive [k]. In contrast, in non-Oirat Mongolian, such as Khalkha Mongolian, the sound that date backs to *k in Proto-Mongolian is realized as the fricative [x]. The results of the survey data demonstrate that the velar obstruents are more frequently realized as the fricative [x] instead of the plosive [k] (which is occasionally realized as the affricate [k͜x]). From a diachronic point of view, the de-plosivisation of the velar obstruents in the Alasha dialect is found to be more likely at the non-word-initial and before vowels e, ü, and ö. This study’s phonetic analysis of the velar obstruents reveals that, among the Mongolian languages, the Alasha dialect is in an intermediate stage of de-Oiratization.