This study looks into the relationship between nomophobia and loneliness, and the effects of smartphone and mobile internet use among adolescents. A total of 301 adolescents were employed for the study and the data were collected via Nomophobia (NMP-Q) and UCLA Loneliness Short-Form (ULS-8) Scales. The study was conducted in a relational survey model using descriptive statistics, ANOVA, Pearson correlation, and linear regression. According to the findings the levels of nomophobic behaviors of adolescents were at a moderate level. While there was not a statistically significant correlation in terms of the duration of smartphone ownership and monthly mobile internet GSM quota, a significant difference was found in terms of the duration of mobile internet ownership, the duration of daily mobile internet use, and daily smartphone checking time. Finally, there was a statistically significant relationship between nomophobia and loneliness, and it can be ascertained that loneliness of adolescents predicts their nomophobia levels to a certain extent.