The syllabic structure in the Hmongic language, Hmu (spoken by nearly one million people), is examined, based on the dialect of Hmu spoken in the town of Yanghao in the Southeast Guizhou Miao-Dong Autonomous District of southern China. The discussion is based entirely on data presented by Wang (1979). From the examination, two rules with the following properties are posited: (1) vowel assimilation to a following consonant; (2) vowel assimilation to a preceding consonant; and (3) assimilation with respect to the feature [high]. The analysis leads to the conclusion that the SPE feature [high] is useful for describing the function of both vowel and consonants in the process of Hmu diphthongization. However, there are several unanswered questions about [high] especially in its interaction with "round" and "back." Contains 13 references. (Author/LB)