The problem that encountered by medical physicists in determining the value of Monitor Unit (MU) for the treatment of palliative cancer is associated to its inefficiency, because the calculation of MU value is still performed manually. The simulation of MU value calculation is purposed to help medical physicists in determining of the MU values both accurately and efficiently. The data which is needed to determine the MU values were the assigned dose from the doctor, the Tissue Maximum Ratio (TMR), the Percentage Depth Dose (PDD) and the Output Factor (OF) values. The determining of the TMR, PDD and OF values needs the data from photo simulators such as field length, field width, and cancer depth. The tabulated TMR, PDD and OF data at energies 6 and 10 MeV were converted into the database. There are two techniques that can be used, such as the Source to Surface Distance (SSD) and the Source to Axis Distance (SAD) technique. The accuration of the MU value from this simulation has a percentage of errors less than 4% when compared to the Treatment Planning System (TPS) using a virtua1 phantom. The result of this simulation is accurate and efficient because the percentage of errors is less than the tolerance limit (5%) as being specified by the International Atomic Energy Agency (IAEA).