In text communication service, mobile instant messenger (MIM) has now moved beyond email, SMS and more. With the popularization of smartphones, MIMs which feature no-cost and convenience such as Kakaotalk, Line, and WhatsApp have grown tremendously. Nowadays, numerous people are interacting with MIM, and the range is being used not only for everyday conversations, but also for business communication. As the use of MIM expands, people getting stress from MIM is increasing. In South Korea, the penetration rate of smartphones is over 91%. MIM is used pervasively even in public societies such as schools and companies, and MIM stress has become a serious social problem. We are currently working on a study to understand the phenomenon and cause of MIM stress.