Social network is a platform for people share their ideas, to meet new friends and to reconnect with old friends. Social networking sites (SNSs) offer people new and varied ways to communicate via the internet, whether through their PC or their mobile phone. They include MySpace, Facebook, Skype, twitter, Hi, LinkedIn, etc. and allow people to create their own profile and to construct and display an online network of contacts, often called ‘friends’. Users of these sites can communicate via their profile both with their ‘friends’ and with people outside their list of contacts. With SNS it is easy to communicate with classmates, discuss class assignment and even submit project to lecturer, watch videos, make comment on friend’s pages etc. This study is focused on the effect of SNS on student academic performance, using Jimma University, Information Science students’ as a case study. It is to study the SNS sites used by students and for the purpose of using and to find out whether they affect their studies or help them to learn easily. This research discusses the history of SNS, development and the users of SNS especially Information Science students in communicating with their friends as well. A detailed questionnaire has been designed to assess the effect of SNS on the Students’ academic performance and administered to 50 students’ selected using a Stratified Sampling Method. The collected data has been analyzed by tables, charts and graphical representation with description. From 50 respondents, Facebook is seen mostly used by the students. They spent more than three hours on SNSs and most of them are using more than three SNSs. 84% of the students are influenced by SNSs on their academic lifestyle so that SNSs affect their academic negatively.