Since the last century, many scholars' efforts have contributed to revealing that Old Chinese was a language in which relatively abundant changes in the form of words took place on the contrary to Modern Chinese. This study discussed ablaut phenomenon, which has been relatively less studied compared with the prefix or suffix. In particular, among 16 groups of cognate words that were presented in the study of Pulleyblank (1973) as words formed by ablaut, this study examined two groups of ― wei 圍(*GwЩl)/ wei 衛(*Gwads) and he 合(*guːb)/ hui 會(*goːbs) that can be verified using Chinese paleography data. In addition, the main vowel discrepancy between yi 抑(*?ŋЩg) and yang 仰(*ŋaŋ?) that was left as a future task in the study of Kim, Jun-soo 金俊秀 (2016b) was also explained as an example that reflects ablaut phenomenon.