When the game is used in mathematics loaming, students take pleasure of game in themselves and communicate through interaction with other students naturally. It is important because the game is activity for intellectual growth and social development. Also students have had affirmative attitude about mathematics by Emu. The communication in mathematics loaming helps that linking informal and intuitive thinking of students with abstract and basic mathematical language and that it also helps changing from the dependent situation to teacher to the self-directive teaming of students. The purpose of this thesis is to effect on extension of mathematical communication ability to the second grade of elementary school students by applying of computational-strategy games. It has conclusion as follows. Application of computational-strategy games had effected on extension of mathematical communication ability importantly. When students have mathematical communication through computational-strategy games, at the beginning, the words which students used was long, incorrect, and unnecessary words. But at the later, students became to use clear, correct concise words as they connect their routine language with mathematical symbol. Therefore we can make sure that mathematical communication ability of the second grade students' is extended by applying of computational-strategy games.