The electric power system used in Indonesia as a whole is a three phase voltage system with alternating current. This three-phase electrical energy is generated by a three-phase generator that is sent through a three phase transmission line. In the process of sending electrical energy from the power plant to the consumer, the voltage must be reduced first. The three phase electrical voltage system of phase R, phase S, and phase T must be balanced, if it is not balanced then a neutral conductive current will emerge. The use of nonlinear loads causes the distortion of sinusoidal waves to cause harmonics. As a result of load and harmonic imbalances that cause inefficient use of electrical energy. This research was conducted to determine the quality of electric power in PKU Muhammadiyah Yogyakarta. Measurements were made on the LVMDP panel, west block panel, and east block panel. Measurement of each panel for 24 hours with 30 minute intervals. Measurements include Frequency [Hz], voltage [volt], total Harmonic distortion (THD) voltage [%], current [ampere], Total Harmonic distortion (THD) current [%], active power [kW], reactive power [kVAR] , false power [kVA], power factor, unbalance voltage [%], and current unbalance [%]. The results of measurements of electric power quality are known that there is a problem with the total value of Harmonic Distortion (THD) current [%] has exceeded the IEEE Standard 519-1992, and unbalance of currents that have passed ANSI Standard C84,1-1995. Harmonic currents and unbalance cause an inefficient use of electrical energy so that they have to pay a loss of Rp. 3,148,027.