This paper explores the properties of users writing styles in online communication, in especially focusing on an instant messenger (KakaoTalk). Through this case study, this paper proposes that identifying different writing styles between generations (20s vs 60s) is necessary for effective intergenerational communication. Considering the properties of spoken and written language, this paper focuses on the four types of writing styles in KakaoTalk: 1) whether to use the title 2) whether to check the spelling 3) whether to use emoticons 4) whether to drop or transform functional elements. This paper collects data from 400 users with a professional opinion-testing agency for survey objectives. This paper analyzes and interprets the results based on a few variables such as generation, sex, and age to verify conclusions. This study will be the start point for improving intergenerational communication.