This paper examined the characteristics that can be seen only in Sino-Vietnamese. The characteristics can be written down as follows: First, all dental-alveolar fricative and affricative initials(精系) were changed into alveolar stops, and alveolar fricative and affricative initials(莊系) and palatal fricative and affricative initials(章系) are distinguished in Sino-Vietnamese. This characteristic reflects Early Middle Chinese. Second, the bilabial consonant of the fourth division of Chongniu(重紐) rhymes was changed into alveolar stop t-, which is the biggest characteristic in Sino-vietnamese. Third, glottal fricative initial(云母) lost its sound and became zero-initial during the qieyun(切韻) period. However, this initial was changed into labiodental initial v- in Sino-Vietnamese. Fourth, Hashimoto Mantaro suggested that the final consonants of Geng she(梗攝) characters would be nasal palatal -ɲ, -c. The final consonants of these characters are preserved in Sino-Vietnamese. This result supports Hashimoto’s theory. This paper also examined the theory that the third division of rhyme 庚 and the third division of rhyme 淸 were in Chongniu relations, and the possibility that the medial sound of the third division of hékǒu rhymes was -wj-. This paper also examined the possibility that the Vietnamese vocabularies of tim(心), tuổi (歲), có (有), and cá (魚) came from Old Chinese.