This study aims to determine the effect of family functioning on loneliness in adolescents who use online games. The research method used is quantitative with simple linear regression analysis techniques. The research respondents were 201 adolescents ages 12 to 16 years old obtained by nonprobability sampling technique using the incidental sampling method. Data collection was carried out with measuring instruments The University of California, Los Angeles Loneliness Scale Version 3 (UCLA) and the Indonesian version of the Family Assessment Device (FAD). The reliability of each measuring instrument is 0.861 for UCLA and 0.921 for FAD The results showed that Ha was accepted and Ho was rejected, there is a significant effect between family functioning on loneliness in adolescents who use online games, it can be seen from the significance value which is 0.000 (p <.05) and the R2 value was 0.146 which means that family functioning affects the loneliness of adolescent online game users by 14.6%. Then the regression coefficient value is -0.185 which means that the effect of family functioning on loneliness shows the opposite direction (negative). Thus it can be concluded that the higher the family functioning, the lower the loneliness experienced by teenagers who use online games.