Abstract: Fast food has become an important part of our diet and the increase in fast-food consumption is likely to continue. Our aim was to study the relationship between fast food and Body Mass Index (BMI) and the pattern of consumption of fast food in female university students. Total of 141 female students from different study levels of Nutrition and Food Science Department, King Saud University (KSU), Riyadh Saudi Arabia were included. A survey questionnaire which contains three sections was used; firstly sociodemographic data, secondly fast food consumptions pattern and thirdly whether students apply basic nutrition knowledge in their selection of food or not. Height, weight and BMI were measured. We found that overweight and obesity were present in 25% of female students. Fast food consumption frequency of 1-2 times per week was high among them (74.5%). There is no significant relationship between fast food consumption, BMI and the pattern of consumption of fast food. There is a significant (p<0.05) positive relationship between increase in size of fish sandwich meal and increase of BMI. However there is no significant relationship between portion size of other food types and BMI. Moreover, we found significant (p<0.05) positive relationship between university study level and the knowledge in explaining why fast food is unhealthy.