In this paper, a maximum power point tracking controller using particle swarm optimization (PSO) is imposed on DC boost converter of a solar photo voltaic system under changing physical conditions. The proposed PSO based MPPT controller guarantees the extraction of maximum power from the solar photo voltaic system by controlling the duty cycle of the DC to DC boost converter. It is ensured by determining the optimal value of current and voltage of solar PV system corresponding to maximum power. The entire system and the controllers (PSO and P&O) are implemented in MATLAB. The results show that even at variable atmospheric conditions, and the proposed controller is able to track maximum power faster as compared to P&O based MPPT controller.