Among front vowels in modern Manchu-tungus languages, [e, æ, œ, and y]-which may be referred to as secondary vowels-did not exist in the 17th century Manchu. The development of secondary front vowels is observed mainly in modern Manchu, spoken in Heilongjiang Province of China, and Sibe, spoken in Xinjiang Province of China. In the present study, we explore the development by employing the data from Chinggeltei (1982) and Yamamoto(1969). We claim that the secondary vowels were developed through umlaut and vowel contraction both of which were first observed in the 18th century Manchu. We found that the changes occurred in Manchu-tungus languages show striking similarities to those occurred in Korean and the Mongolian languages. The genealogical relationship of Korean to other languages is not well established. One of the reasons may be that the earlier methodology was not suitable to establishing the relationship. The similarity shown among those languages reminds us of the fact that there is strong tendency for similar development among daughter languages. So it is one way of searching genealogical relationship to find similar developments among neighbouring languages.