In general it is said that the starting point of present-day Korean is the threshold of 20th century. It seems that there are many criteria drawing a line between the modern Korean and present-day Korean. But as to the phonological area, features distinguishing present-day Korean from modern Korean have not been presented sufficiently. The monophthogization of ''oy, uy'' is the most characteristics change, but less important. The method for the historical phonology of present-day Korean is different from that of the earlier period of Korean. For example, the records of documents is the most important in the study of middle Korean or modern Korean. But it is no longer valid for the present-day Korean. In contrast with earlier Korean, the field work of dialects are the core in the present-day Korean. In addition, language norm affects phoological changes more vigorously.