The researcher focuses on impact of social media marketing of e-retailing companies on buying behaviour of consumers with reference to age group 18-45 years in Trichy attempts to focus how e-retailers can leverage social media to penetrate their market and reach-out their customers. The primary data required for this study were collected through structured questionnaire by using simple random sampling and the secondary data were collected from journals and websites. The Collected data were analysed by using statistical tools. The results of this study highlights impact of social media marketing strategies of e-retailing companies on buying behaviour of consumer and factors influencing consumer to purchase product from online.