Background  and  Purpose: The purpose of this study was to investigate the mediating role of loneliness in the relationship between parent-teenager conflict and Internet addiction in the second high school students of Mashhad.
Method: The fundamental and descriptive-correlation research method was based on structural equation modeling. The statistical population includes all students of the second secondary school in Mashhad who were studying in the academic year of 1402-1403, which were selected using the multi-stage cluster random sampling method of the 1st education district of Mashhad, and then 4 high schools (2 girls' high school and 2 boys' high schools) and a sample of 200 people was selected from  among  them.  In order to collect data, Deshiri et  al.'s  Loneliness Questionnaire (2007), Strauss’ Parent-Child Conflict Questionnaire (1990) and Young’s Internet Addiction Questionnaire (1996) were used. Data were analyzed by SPSS23 and AMOS software and by Pearson correlation test and structural equation modeling (path analysis).
Result: The results of Pearson correlation analysis showed that there is a significant positive relationship between parent-adolescent conflict and feelings of loneliness with Internet addiction. The results of the path analysis showed that the parent-adolescent conflict has a positive and significant effect on Internet addiction and students' feelings of loneliness. Also, the feeling of loneliness has a positive and significant effect on students' internet addiction. The results of path analysis showed that loneliness plays a mediating role in the relationship between parent-adolescent
conflict and Internet addiction.
Conclusion:  A  person  who  feels  lonely  or  generally  does  not  have  the  ability  and  possibility  to  establish relationships with others in the real world, or his interpersonal relationships for various reasons, such as the fact that he enters the conversation with negative expectations and predictions, and also to The reason for the lack of social skills necessary to establish and maintain close friendships has been damaged. Therefore, to make up for it, he turns to the Internet and cyberspace communication where communication with others is much easier than in the real world.