This research examines the influence of social media advertising and influencer marketing on Generation Z purchasing decisions within the fashion e-commerce sector in the West Coast Region of The Gambia. The study aims to: (1) analyze the impact of social media advertising on Generation Z purchasing decisions; (2) assess the effect of influencer marketing on Generation Z purchasing decisions; (3) evaluate the extent to which impulsive buying mediates the relationship between social media advertising and Generation Z purchasing decisions; and (4) determine the extent to which impulsive buying mediates the relationship between influencer marketing and Generation Z purchasing decisions. This research utilizes a quantitative methodology and a descriptive approach. The study sample comprises 130 Generation Z respondents, aged 18 to 30, from the West Coast Region of The Gambia. Data analysis was conducted using SmartPLS 4 and Partial Least Squares-Structural Equation Modeling (PLS-SEM) techniques. The research is grounded in the Stimulus-Organism-Response (S-O-R) model, which explains how digital marketing stimuli elicit psychological responses that influence consumer purchase behavior. The findings indicate that social media advertising and influencer marketing are significant determinants of Generation Z purchase decisions in fashion e-commerce. Additionally, impulsive buying behavior mediates the relationship between digital marketing stimuli and purchase decisions, demonstrating that digital content and influencer marketing can prompt impulsive purchases. These results underscore the importance of advertising and influencer marketing in shaping consumer behavior. The study provides actionable digital marketing recommendations for fashion e-commerce marketers and retailers in The Gambia and comparable developing economies, offering insights into strategies tailored to Generation Z consumers. Keywords: Social Media Advertising, Influencer Marketing, Impulsive Buying, Purchasing Decisions.