ABSTRACT Objectives: Investigate the prevalence of Rh and the K antigens and their phenotypes in the red blood cells of blood donors in Riyadh, Saudi Arabia. Methods: This is a retrospective study. The five principal Rh antigens (D, C, c, E, e) and the Kell antigen from the Kell blood group were tested in 4,675 random samples collected from four blood bank centers in Riyadh. Data were collected for seven weeks (from January 4, 2019 to February 28, 2019). Antigens were tested using the TANGO Optimo system. Results: We found that approximately 86% of the donors had the D antigen, 66% had C, 78% had c, 26% had E, 97% had e and 14% had K. The most common Rh phenotypes were R1r (31%) and R1R1 (22%). Conclusion: The differences in the results between the study population and other populations, such as Caucasian, Indian and African populations indicate the importance of establishing a population-specific database.