With the development of technology and popularization of Internet, the use of instant messaging software has become one of the main pathway in interpersonal interactions. However, instant messaging software LINE is quite often applied in parent-teacher educational scene. Although it has brought many conveniences, it has also caused quite a few problems. Therefore, how to make the best of efforts in LINE APP for communication will be an essential issue for parents and teachers to learn. The purpose of this study was to investigate the current situation of elementary school homeroom teachers using instant messaging software LINE as a parent-teacher communication tool. Case study design was used. The participants in this study were chosen on a convenience sampling to use the qualitative interviews from each lower, intermediate, and higher grade teachers and parents in Taoyuan public elementary school. An interview outline conducted a semi-structured interview which combined SWOT analysis for asking questions in order to figure out the SWOT components in using LINE as a communication app. The results were listed as follows: 1.Sending text messages and pictures was the main function of using LINE APP in parent-teacher communication at elementary stage. 2.The message contents focused on the daily-life performances of children and individual emergency situations. 3.The acceptable contact time for parent-teacher communication was from school time to ten o’clock at night. 4.Parent-teacher communication happened after-hours due to the urgency, importance and privacy. 5.Convenient, prompt feedback, a large number of users, and free of charge were the primary reasons of using LINE APP for parent-teacher communication. 6.Various functions were used for parent-teacher communication which depended on the urgency or importance. 7.The main strengths of LINE APP were time and energy savings as well as interactions increased among parent-teacher-student. 8.The main opportunity of LINE APP was to share educational related websites resources. 9.The main weakness of LINE APP was the lack of concept of time from users. 10.The main threat of LINE APP was the disputes triggered by the group. Thus, the researcher offered some suggestions for reference according to the research findings to elementary teachers and parents for future research.