--- - |2 Abstract Since the September 11, 2001 terrorist attack against the World Trade Center in New York City, terrorism has become one of the most distressing large‐scale societal threats. The March 22, 2016 terrorist attack in Brussels, the capital of Belgium undermined the collective sense of perceived security and social cohesion. The present research investigates Belgian civilians’ (N = 202) terrorist threat perception, personal emotions, and the role of perceived emotional synchrony in the construction of the perceived socioemotional climate in Belgium. The main purpose of the current study was to examine the role of perceived emotional synchrony emerging in collective gatherings as a regulatory mechanism improving the perceived socioemotional climate of the country. Additionally, the precise components (personal vs. collective) shaping the perceptions of terrorist threat were also examined. This study was conducted by a questionnaire during the collective gatherings in Brussels 1 week after the terrorist attack. The main results suggest that the terrorist threat has been perceived at the collective level rather than at the personal level. Furthermore, the perceived emotional synchrony with others mediated specifically the relationship between positive personal emotions and the perceived positive socioemotional climate in Belgium. Such findings point to the importance of considering the perceived emotional synchrony in order to provide a better understanding of lay people's psychosocial responses to terrorism and the subsequent construction of collective macro‐social phenomena in post‐terrorist contexts. - Journal of Applied Social Psychology, Volume 48, Issue 9, Page 477-487, September 2018.