The diurnal variation of cosmic rays (CR) is an important tool for understanding the fundamental physics of the Earth's heliosphere and magnetosphere. It depends on complex processes in the interplanetary magnetic field (IMF), magnetosphere and other regions, depending on the detector location on Earth. Daily variations can be characterized by magnitude (maximum value) and phase (time of maximum magnitude). In this study, the first available data from the King Abdulaziz University (KAAU) muon detector was used to investigate the diurnal amplitude and phase of CR muons. KAAU is located in Jeddah (Rc = 14.8 GV) in western Saudi Arabia and has been operating since 2007. The magnitude and phase of daily fluctuations in CR muons were calculated and determined. Although the diurnal fluctuations of CR muons are more complex than those of neutron monitors, results comparable to those previously described were found.