Background: Social networks influence the lives of individuals and communities. They have several advantages; however, they have many disadvantages including its adverse effect on social life and academic performance of students. They are reasons for time-consuming, individuals can even addict these sites. Aim of the work: this study aimed to determine impact of social media on academic performance and social relationships as well as factors associated with social media and pattern of using social media. Methods: This was an observational cross-sectional study which was conducted in Jazan University; it included 205 (45.1%) male students and 250 (54.9%) female medical students. A questionnaire was used to perform this study. SPSS was used to analyze data. Results: The present results showed that the most common used sites were facebook (53%), 65.9% of students used social networks for more than three years, 58.5% used these sites for 2 to 4 hours. Gender was a significant factor regarding using Facebook and WhatsApp (P-value=0.001, 0.004 respectively), the only significance was found between the different academic years was regarding WhatsApp (P-value=0.001) which was commonly used by fourth-year students (46.1%). Both numbers of hours and using social media during lectures influenced study level (P-value=0.01, 0.021 respectively). Conclusion: The most common social site used was Face book and the social media affected the academic performance of students negatively. Social media has both positive and negative effect on social relations.