LiCoO2 is one of the most important cathode materials for high energy density lithium ion batteries. The compressed behavior of LiCoO2 under high pressure has been investigated using synchrotron radiation x-ray diffraction. It is found that LiCoO2 maintains hexagonal symmetry up to the maximum pressure of 30.1 GPa without phase transition. The elastic modulus at ambient pressure is 159.5(2.2) GPa and its first derivative is 3.92(0.23). In addition, the high-pressure compression behavior of LiCoO2 has been studied by first principles calculations. The derived bulk modulus of LiCoO2 is 141.6 GPa.