Background: Obesity was reported to be highly prevalent in KSA. Bariatric surgery is considered as the most effective, beneficial, and permanent method for treatment of obesity and decreasing the long-term mortality Objectives: Evaluating the knowledge and beliefs about the safety and effectiveness of bariatric surgery among adult Saudi population.        Methods: A questionnaire based on cross-sectional study was distributed among 790 adult Saudi population form January 2017- June 2017. The questionnaire was based on 4 aspects including subject's demographics, anthropometric measures, knowledge about obesity and its causes and beliefs about Bariatric surgery. Results: Overweight and obesity were found to be high among the studied population. The most common causes for obesity were bad life style habits and genetic factors. There was a good knowledge about obesity but low favorable beliefs about bariatric surgery as 55.7% of subjects have non-favorable beliefs about the Bariatric surgery and 44.3% have favorable beliefs about the surgery. The favorable beliefs about bariatric surgery were significantly associated with female gender and subjects having high BMI scores. Conclusion: The knowledge of subjects about obesity and its preventive measures were high but the favorable perceptions about Bariatric surgeries were low. These results indicated that efficient educational programs about obesity and Bariatric surgeries are needed for control of obesity and its complications as well as increasing the availability of weight loss surgeries.