This study aimed to reveal the impact of social networking sites on the purchase decision of the Libyan consumer and the time and effort it saves in evaluating between the available alternatives, and knowing this effect on each stage of the purchasing decision. The study community consisted of all users of social networking sites in Tripoli who depend On these sites to purchase their products, The study sample consisted of (450) consumers and (430) of them responded to the questionnaire but only (400) were found valid for analysis, with 85% response rate. Statistical package for social sciences (SPSS) was used to analyze and test the hypothesis, The study results indicated that there is a high impact of social network on Purchasing decision making at all stages: the perception of the consumer of the product that was advertised through social networking, to help consumers to fined different alternatives to satisfy their needs, the ability to choose the suitable product, the purchase of the product, evaluate the decision after the purchase stage. The study recommended : Companies that advertise on social networking sites must provide the required amount of information about the characteristics of the products they are advertising. In line with the constant change in consumers' desires, companies must clarify the true prices of products advertised on social networking sites, and companies must adhere to the timing of product delivery and provide appropriate maintenance programs to the consumer . Key words: Social Media , purchasing decision , Internet advertisin