Abstract The aim of this study is to determine the influence of Electronic Word-of-Mouth (eWOM) in Social Networking Sites (SNS) towards online purchase intention of youth, through several variables relating to e-WOM source characteristics (Source's expertise, 3 similarity, trust); also both positive and negative valence of e- WOM. To achieve those targets, an electronic questionnaire was designed and distributed to a purposive sample from users of social networking sites Facebook and Twitter of Egyptian youth aged between 18-34 years, and 682 questionnaires were valid for a statistical analysis. The results of the data analysis has shown by SPSS statistical package that there is a positive impact of the electronic word-ofmouth as assessed by all dimensions combined on intentions for buying online at 56.1%. In addition, the study showed that 17% of the variability of the online purchase intentions of the youth could be referred to the variability in the electronic word-of-mouth Source's expertise. While the explanatory and predictive ability of the similarity between the sender and the receiver in the online purchase intentions reached 9%. The results revealed also that there was a significant effect due to the trust in the source of the electronic word-of-mouth on the online purchase intentions of the youth, 20% from variability in the purchasing intentions of youth online is due to the variability in trust from e-WOM source. The study could realize that 25% of the variability of online purchase intentions of the youth was referred to the negative electronic word-ofmouth, while the positive electronic word-of-mouth was responsible for only 16.5% of the same variability.