Social media growth has changed consumer behaviour from offline consumption to online consumption. Social media provide opportunities for information sharing, and can routinely find out what others are doing and talking about. Instagram is a social media platform with visual elements and features that can provide a more comfortable space for social interaction and a stronger sense of community or connection between fellow users. The rapid growth of social media plays a vital role in creating feelings of fear of being left behind or fear of missing out (FoMO). FoMO behaviour can impact consumption and give rise to a new concept, "Fomsumerism". This study aimed to determine the effect of Instagram content quality on fomsumerism behaviour mediated by emotional response variables. This type of quantitative research uses non-probability sampling methods and purposive sampling techniques on 150 respondents. An online survey collected data and analyzed using SEM-PLS through the SmartPLS application version 3.9.9. The study results show that the quality of Instagram content positively and significantly affects fomsumerism behaviour. Emotional response as a mediating variable plays a partial mediation role so that the Instagram content quality variable can affect the fomsumerism variable directly or indirectly.