To improve image quality (IQ) and reduce dose in x-ray fluoroscopy, we have developed a new method for optimizing x-ray conditions such as x-ray tube voltage, tube current, and gain of the detector. This method uses a Monte Carlo (MC)-simulation database for analyzing the relations between IQ, x-ray dose, and x-ray conditions. The optimization consists of three steps. First, a permissible dose limit for each object thickness is preset. Then, the MC database is used to calculate the IQ of x-ray projections under all the available conditions that satisfy this presetting. Finally, the optimum conditions are determined as the ones that provide the highest IQ. The MC database contains projections of an estimation phantom simulated under emissions of single-energy photons with various energies. By composing these single-energy projections according to the bremsstrahlung energy distributions, the IQs under any x-ray conditions can be calculated in a very short time. These calculations show that the optimum conditions are determined by the relation between quantum noise and scattering. Moreover, the heat-capacity limit of the x-ray tube can also determine the optimum conditions. It is concluded that the developed optimization method can reduce the time and cost of designing x-ray fluoroscopic systems.