In assessing the power system, the most important issue is the system behavior when the system is affected by a disturbance In some plants in case a small event, oscillations are created that are not easily damped and this lack of damping causes the power plant shut down. So, conditions should be set such that the power plant damps the oscillations as soon as possible and returns it to the stable conditions. In this paper, microcontroller-based power system stabilizer (PSS) is designed that increases the single machine dynamic stability of the power system connected to an infinite bus by improving damping in the low frequency oscillation. The system stability is investigated by the eigenvalues and the results of dynamic simulations are provided in the time domain. Programmable interface controllers (PIC) have been used in designing digital PSS; then the continuous time domain PSS is converted to discrete time domain PSS and finally it is implemented on the microcontroller chip.