The purposes of this paper are to examine changes of declarative sentence`s final endings focusing on the examples of modern Korean, divide them by types and find tendency related to changes. This paper can be summarized as follows. ① The change types of language are two things; ``change of form``, ``creation of final endings``(``condensation`` and ``cutting``). ② The ``change of form`` is to change language form because of the sound change. Its examples are ``-ㄴ뎌>-ㄴ댜`` ``-괴여>-괴야`` ``-ㄹ셔>-ㄹ샤`` ``-고나>-구나``, etc. ③ The ``condensation`` is that morphemes are condensed because of the sound change and function change. Its examples are ``-ㄹ러라, -ㄹ로다, -ㄹ로다, -ㄹ다, -로쇠, -ㄹ쇠, -ㄹ돠, -올시다, -습디다``, etc. ④ The ``cutting`` has three forms; ``cutting by slurring the end of the sentence``, ``cutting by saving efforts`` and ``cutting after changing function``. ⑤ The ``cutting by slurring the end of the sentence`` is closely related to honorific method. It has two forms; cutting of morphemes (example, -□, -뇌, -외, -데, -니, -리, etc.) and cutting of clause (example, -지, -ㄴ□, etc.). ⑥ The ``cutting by saving efforts` is a cutting for reducing the efforts to speak. It eliminates ``-고 하-`` and its example is the message forms such as ``-다네, -다데, -단다, -다더라, -답디다``. ⑦ The ``cutting after changing function`` is to change the function of non-final endings and become final endings by cutting escorting elements. Its examples are ``-□`` ``-소/오``, etc.