Abstract.In the open source software (OSS) development environment, a communication time-lag among developers is more likely to happen due to time differences among locations of developers and differences of working hours for OSS development. A means for effective communication among OSS developers has been increasingly demanded in recent years, since an OSS product and its users requires a prompt response to issues such as defects and security vulnerabilities. In this paper, we propose an analysis method for observing the time-lag of communication among developers in an OSS project and then facilitating the communication.