Nasal vowels are widely attested in the sound inventories of the world's languages. It is usually assumed among phoneticians and universalists that the historical development of distinctive vowel nasalization consists of two ordered processes, i.e. vowel nasalization and nasal deletion, that is, the vowels become contextually nasalized before a nasal consonant at some stage in history; then the nasal ending is subsequently lost and vowel nasalization on the preceding vowel becomes distinctive and phonological. However, not much work has been done to reconsider or to provide phonetic evidence for or against this two-step account. For instance, the manner and motivation of the process of nasal deletion, which is generally assumed as a simple and one-step change, has not been studied in any detail. In this connection, we examine in the present study the aerodynamic characteristics of vowel nasalization in Xiangxiang Chinese, a representative of the Old Xiang Dialects of Chinese, which has a rich set of nasals, nasalized and nasal vowels (both monophthongs and diphthongs) and allows combinations of oral and nasal consonants and vowels, and discuss the implications of the current results as well as those from studies on vowel nasalization in other languages for the theories of sound change. In particular, our intention is to test the two-step account and to reconstruct the processes involved in the historical development of nasal vowels.