A qualitative study was conducted to investigate the relationship between improvisation and organizational learning for a case of the Mobile Crisis Team (MCT), a mental health emergency response agency. It is found that two types of improvisation in MCT, such as interactional and role improvisation, require continuous interpretation of subtle signals and redefinition of the roles related to those of other participants at the scene. The analysis also identifies key antecedents such as unpredictability, urgency, flexible role structures, minimal procedures, and available resources. Finally, lessons learned from improvisational activities are integrated into the system through three types of learning: learning by doing, learning by sharing, and learning by collaborating. Based on these findings, this paper suggests that improvisation in emergency response, for which the nature of the work inherently involves high risk and unpredictability, is inseparable from organizational practice. Improvisational action in this organization should be understood as an active sense-making and role-making process by organizational members in the moment. This active engagement of participants postulates that there is shared understanding of role structures within the community of practice.