The author has studied the dynamics of toner and carrier particles in a two-component magnetic brush development system used for electrophotography using a direct observation technique and numerical simulation method. We have manufactured a mock-up apparatus consisting of a pseudo-photoreceptor drum, development sleeve, and stationary magnetic roller. The image was created on an insulated film electrode pasted onto the drum. The behavior of the toner and carrier particles has been observed directly using a high-speed microscope camera and calculated using 3D distinct element method that includes the calculation of the magnetic interaction force and the transient electric conduction in carrier chains. Parameters for the experiment and calculation were the diameters of toner and carrier particles, toner/carrier concentration, development gap, development voltage, speed ratio between the photoreceptor drum and development sleeve, waveform and magnitude of superposed ac development voltage, and distribution of magnetic field created by the magnetic roller. Optimum conditions for realizing high image quality printing have been proposed considering all the various factors together.