Abstract: Background: Internet is an important tool of modern society used frequently for communication and information sharing and become an integral part of the daily lives for every one even child. Internet addiction in children is a mental disorder that negatively affects their life and their health. Aim: to assess negative health effects on addiction of internet among primary schools students in Zagazig city. Design: A Cross-sectional descriptive design. Setting: at six primary schools at Zagazig city. Subjects: 300 students were selected using a multistage random sample technique. Tools: Interview Questionnaire sheet, Internet Addictive Behavior Scale, Negative Health Effects of Internet Use and Knowledge related to internet. Results: the mean age of the students was 17.2±0.824, 76.80% of them were highly internet addicted and the majority of related contributed risk factors for being addicted to internet were Online gaming internet, Entertainments ,Build relationships with others , and Using social networks, with percentage (99%, 95.3%, 88.6%, and 84.6% respectively), there were highly statistical significance relation between total internet addiction degree and contributed risk factors to internet addiction regarding difficulties to relate socially, availability/ accessibility to use internet , using social networks at (p-value = 0.02*). Also, 75.7% of them had unsatisfactory total knowledge score related to internet addiction. Additionally there were highly statistically significant positive correlation among students total score of total internet addiction and total negative health effects of internet addiction (r =.0638**), Conclusion: most of the students had high degree of internet addiction, also they were highly negatively affected on their physical, social, cultural, economic, and psychological health related to excessive internet use. Recommendations: organize training programs involving parents, schools, social workers and psychologists of educational organization to raise public awareness on proper Internet use and increase awareness among primary students about Internet addiction and its negative health effects. Key words: Negative health effects, Internet addiction, Primary schools students, and Communication.