Obesity in combination with unhealthy life style may increase the risk of chronic diseases. Objectives: This study aimed to determine the gender difference of body composition and respiratory functions among medical students and its relationship with their life style. This study was performed on 165 male and female students. Body mass index (BMI) and body composition parameters were assessed using bioelectric impedance. Respiratory function, fasting blood glucose, lipid profile and sex hormones were assessed. A questionnaire was distributed among the participants to determine the association between the different variables and risk of obesity. The rate of overweight and obesity among male and female students were 16.9% and 15%. Overweight and obesity among male and female students were (24.6% and 21.3% vs. 12.1% and 11.1 %, respectively). Total fat mass and total fat percentage were higher in female students, whereas, free fat mass was higher in male students. The total fat percentage exceeded its normal limits in overweight and obese females and in 11.7% of those with normal BMI. High levels of total fat% were observed in obese and in 66.7% of the overweight male students. Thus, 37.7% in male and 35.6% in female students were obese according to the body fat percentage when used for defining adiposity rather than BMI. Forced vital capacity (FVC) was increased in male students and a positive correlation between FVC and free fat mass among male students was found. These data demonstrate that overweight and obesity are a problem among medical students of Taibah University.