The early 20th century is a period of time when Korea confronted with the surging waves of modernization, and made a variety of internal reactions. The Korean language, not immune to the upheaval, also experienced new changes and gradually gained characteristics of today's Korean. Although scholars have not yet fully agreed upon the time division of Korean, Gabo reformation (1896) is usually considered to be the beginning of modern Korean. Thus, the early 20th century was also the beginning of modern Korean. Phonological, lexical, and grammatical characteristics of modern day Korean began to appear during this period of time. Phonologically, the 10 vowel system was established, glottal sounds and aspirated sounds increased, vowel harmony declined. Phenomena such as vowel raising, front-vowelization, monophthongization, and the word-initial rule appeared. Meanwhile, hangul-Chinese mix writing became common practice, and hangul-only writing also started to take place in narrative writing, and elements of spoken language began to reflect in written language. All those pointed to the unification of written and spoken language. Under the influence of modernization, a great amount of new words appeared. Especially, Japanese and other foreign words flooded in in great quantities. Grammatically, '-eos-(-엇-), -neun-(-는-), -ges-(-겟-)' trichotomy system of tenses was established, and hearer-oriented honorific system also formed a binary system of 'hasoseo(하소서), hasibsio(하십시오), hao(하오), hage(하게), haera(해라)' and 'hae (해), haeyo(해요)'. In word formation and sentence construction, the use of '-gi(-기)' became more frequent than '-eum(-음)', while '~geot(~것)' also significantly increased. In negative, causative and passive expressions, the use of long form, which has fewer restrictions than the short form, became more frequent. A tendency towards simplicity appeared. In the same vain, long and complex sentences with several clauses tend to be avoided. Instead, short simple sentences became more favorable. Korean linguistics scholars should pay closer attention to the modernization period, which includes the early 20th century. In order to fully understand today's Korean language, more thorough research on this immediately preceding period is necessary.