Obesity is a worldwide public health problem affecting all levels and age groups within the society. Health-related behaviors can negatively affect adolescents' health which contributes to the main causes of morbidity and mortality in this age group. Early identification of health risk behaviors during adolescents are considered to be an important element in the prevention of obesity. Aim: to identify the relationship between body mass index (BMI), health related behaviors and obesity among female adolescent students. Design: a descriptive design was used . Setting: The study was conducted at Technical Institute of Nursing, Ain Shams University. Sample: Simple random sample of 100 female adolescent students from the previously mentioned setting Tools of data collection: included a structured interview questionnaire to assess student's body mass index and health behaviors related to obesity Results: The results showed that less than half of students were normal weight (47%) compared to 39% for overweight and obese and 14% for underweight. The most common health problems as reported by the students were snoring during sleep 14%, anemia 13%, back & knee pain 11%, headache and high blood pressure 10%, diabetes and bronchial asthma 6%. Adolescents had some unhealthy behaviors regarding eating pattern, technology usage, exercise programs. There is a significant correlation between students' body mass index and their eating pattern. As regards students' body mass index and their technology usage, television watching was significantly associated with overweight and obese students than normal weight and underweight students. It was clear that the majority of participants reporting that they use internet more than 3 hours per day and they eat while using the internet. Only 19%of overweight and 16.7% of obese students have exercise program in compared to 57.1% of underweight and 72.3% of normal weight students instead of the majority of the sample did not have any barriers to regular exercise. Conclusion. The study concluded that, there was a strong relationship between body mass index, health related behaviors and obesity among female adolescent students. A high prevalence of them had unhealthy behaviors related to dietary pattern, usage of technology, exercise programs. Recommendations: The study recommended that there is a need for application of educational programs regarding healthy behaviors to reduce the tendency of overweight and obesity among adolescent students.