Social isolation is one prevalent social deficiencies among adolescents. Reasons of social isolation in adolescents are not clear yet. One of the variables that have attracted researchers in recent years to the etiology of social isolation is the dependence on new communication technologies, especially the Internet. This study aimed to determine the relationship between cyberspace dependency and social isolation in adolescents. This study conducted with a survey and cross-sectional design. Statistical population was high school students in Yazd. 535 (218 male and 317 female) adolescents selected using proportional stratified sampling. Instruments of data gathering are: Internet Addiction Test (IAT); and The UCLA Loneliness Scale-version 3 (UCLALS-v3). Cyberspace dependency prevalence rate in this research was 21.7%. Significant difference were found between normal and dependent to cyberspace users, regarding the general social isolation (P < .01); and components of isolation (P < .01); relational association (P < .01); and collective association (P < .05). Hierarchical multiple linear regression analysis showed that cyberspace dependency, explained for 12.2% of the variance of social isolation. Cyberspace dependency is a main risk factor for adolescentchr('39')s social isolation and increases the risk of social isolation among adolescents. According to this result, preventive behavioral and cognitive interventions are necessary in order to change the internet use pattern and reducing the social isolation among adolescents.