Background: the Internet has become an important tool for social interaction, information, and entertainment. Studies have shown that the percentage of students using the Internet has increased dramatically. However, as the Internet has moved into homes, schools, Internet cafes, and businesses, there has been a rapidly growing public awareness of the potential adverse effects arising from excessive, maladaptive or addictive Internet usage, which are a condition also known by terms such as problematic Internet use (PIU), Internet dependence and pathological Internet use. Aim of the study: 1- To determine the general characteristics of Internet users among Al-Azhar under graduate university students in Cairo. 2- To explore the problematic Internet use (PIU) among under graduate university students based on the Internet activities . 3- To investigate the difference between males and females regarding PIU. Materials and methods: a cross sectional study was conducted on a sample of 600 undergraduate university students including both scientific and literary collages of Al-Azhar Universities for girls and boys in Cairo. This sample was chosen randomly through on line questionnaire. All participants voluntarily participated in the present study to identify the extent of problematic Internet use among university students. On line self-administered questionnaire that designed to include different items. Results: female students had significantly lower PIU levels on alldimensions (i.e., social comfort, loneliness/depression, diminished impulse control anddistraction) than those of  males. Furthermore, the results reveal that the students who use internet frequently (3-6 hours/day) and those who use it for entertainment (e.g., game), chat, news (policy or sports news) and social networking purposes have significantly higher PIU levels on all dimensions than the students who use it for less than 3 hours/day or for scientific purposes. Moreover, multiple regression analyses reveal that gender and time spent online daily are significant predictors of PIU and its all dimension except for diminished impulse control only time spent online daily is the predictor. Conclusion: males are more at risk than females in terms of problematic Internet use. The effect of duration of daily internet use on cognitions about PIU was found to be significant in all analyses. Recommendation: the students should be informed about the association between long use of internet /day and PIU to protect them from negative consequences PIU.