Organ transplantation is a lifesaving treatment for patients with end-stage organ failure. Despite the advanced medical science and technology, shortage of organs had led to a growing gap between the demand for organs and the number of donors. With a limited number of studies on the subject and based on those findings, the public knowledge and attitudes must be assessed to understand more clearly that why many people are opposing donating their organs in Saudi Arabia. The objective of our study was to assess the knowledge and attitude of the adult population toward organ donation in Saudi Arabia. This was a hospital-based cross-sectional study where the information was collected using a self-administered questionnaire in Al-Kharj, Saudi Arabia. The questionnaire was distributed in both King Khalid Hospital and Prince Sattam Bin Abdulaziz University Hospital, and data gathered analyzed by Statistical Package for Social Sciences (SPSS version 20.0). There were a total of 403 respondents. Nearly 35.6% did not have the knowledge that organ donation is legal in the KSA. Almost 97% did not know where to go if they want to become donors. All of who were willing to donate, the most common reason was to save someone's life (92.7%). Body distortion (39%) and fear of health complications (35%) were the most common causes people opposed donation. It was suggested that, in order to increase the awareness for organ donation, the important role of health workers and hospital displays should be immediately addressed and public lectures should be held on regular basis. Information regarding organ donation should be incorporated with clear messages in various mass media.