This dissertation analyses the effect of the social media advertising strategies employed by Zara and H&M on customer reactions such as purchase intention and brand loyalty. Three social networking services, namely Facebook, Twitter and Instagram have been selected for the purpose of this study. Primary data was collected from 100 customers of Zara and 100 customers of H&M by means of self-administered questionnaires. In turn, secondary data was obtained from websites, empirical articles and journals. The research findings suggest that social media advertising strategies have a more considerable impact on customer loyalty and attitudes comparing to traditional media. There is a strong correlation between Zara’s and H&M’s social media strategies such as display ads on Facebook and photo posting on Instagram and consumers’ intention to buy. Furthermore, consumers’ loyalty to the fashion brands is predicted by video posting on Instagram and Twitter. The lack of generalisability is the key limitation of this project since its outcomes are only relevant to Zara and H&M. The researchers who investigate social media advertising and its impact on consumer behaviour may be interested in this dissertation.