Some things related to a person’s behaviour and preferences will be linked to his behaviour as a consumer. Technological improvements in this era, such as the internet and social media spread, have become an addiction and formed an understanding that social life is needed. However, unfortunately, what is produced on social media does not all have good results. One of them is the phenomenon of FoMO or Fear of Missing Out. This study aims to get a picture of Consumer Buying and Post-Purchase Behaviour, which in this case is Generation Z shoppers on E-Commerce, as the impact of the FoMO phenomenon. This study uses 14 variables in it, namely social self-efficacy, consumer susceptibility to interpersonal influence, social media addiction, social media self-control failure, novelty seeking, self-esteem, FoMO, the theory of planned behaviour, purchase intention, buying behaviour, and post-purchasing behaviour. The methodology is quantitative research, with the analysis method used being PLS-SEM with SmartPLS 4.0. Data analysis shows that all indicators and variables are valid and reliable. The prediction accuracy of the existing models is also good. Based on the survey data, most respondents feel that FoMO has affected their lives, with a score of 5-6 on a Likert scale of 6, indicating a high effect. Also, based on the analyzed data from questionnaire responses, four paths have the most substantial influence, buying behaviour towards post-purchasing behaviour, fear of missing out on subjective norms, purchase intention on buying behavior, and consumer susceptibility to interpersonal influence on FoMO.