Nomophobia, a type of technological addiction defined as the fear of being deprived of a smartphone, is quite prevalent in young individuals with the widespread use of mobile phones. This study aims to determine the nomophobia level of secondary school 8th-grade students. The effect of nomophobia on academic achievement was investigated by comparing the detected nomophobia levels of the students and the High School Entrance Exam (LGS) scores. These effects on LGS scores were determined by gender, parental attitude, parental education level, smartphone usage purpose, daily smartphone checking frequency, whether or not to carry a charger, areas where the smartphone is mostly used, and checking the smartphone before going to sleep. For this purpose, a correlational survey model was used in the study. The "Personal Information Form" and "Nomophobia Scale" were applied during the 2019-2020 academic year. According to the results of the research, nomophobia in secondary school students differs according to gender, the purpose of using a smartphone, the areas where the smartphone is mostly used, whether or not to carry a charger or not, whether or not to have a smartphone with them before going to sleep; while parental attitude, parental education level, daily smartphone checking frequency doesn't differ their nomophobia. It was determined that the students had moderate nomophobia levels, and the nomophobia sub-factor scores differed according to students' LGS scores.