A phonetic study of vowel devoicing in the Shanghai dialect of Chinese explored the phonetic conditions under which the high, closed vowels and the apical vowel in Shanghai are most likely to become devoiced. The phonetic conditions may be segmental or suprasegmental. Segmentally, the study sought to determine whether a certain type of pre-vocalic consonant is more likely to cause the following vowel to devoice. Suprasegmentally, it sought to determine whether a certain tone category is more likely to cause the vowel to devoice. The study also investigated whether the position of the syllable in a polysyllabic compound constitutes a conditioning factor for a vowel to devoice, and whether the rate of speech has an effect on vowel devoicing. The speech of a male native speaker reading a word list with specific bisyllabic and polysyllabic compounds was subjected to spectrographic analysis. Results are analyzed and conclusions are drawn. Substantial appended material includes the lists of compounds, translations, tone patterns, and speech rates, a 16-item bibliography, and the spectrograms. (MSE)