This research deals with improving the efficiency of solar photovoltaic (PV) power systems using a Fuzzy Logic Controller (FLC) for Maximum Power Point Tracking (MPPT), to control the duty cycle of DC-DC Voltage Converter, to achieve the photovoltaic system works at a Maximum Power Point under different atmospheric changes of the solar insolation and ambient temperature. In this context, this research presents a new model for FLC developed in Matlab/Simulink environment. The proposed model for the controller is based on the conventional Perturb and Observe (P&O) technique. Where, in similar to the conventional P&O technique, the changes in the Power and tension of photovoltaic power system, are considered as the input variables of the proposed controller, while the output variable is the change in the duty cycle. The main advantage of the developed controller FLC, based on the considering the change in the duty cycle has a Variable Step Size, and directly related to the changes in the power and tension of the Photovoltaic system. Which make it possible to overcome the problem of fixed Step Size in the change of the duty cycle in the conventional MPPT- P&O Controller based on P&O technique. The MPPT- P&O Fuzzy, works by a variable step size achieve a fast speed response and high efficiency for tracking the MPP point under sudden and rapidly varying atmospheric conditions, compared with the conventional MPPT- P&O. The simulation results completed in Matlab/Simulink environment, showed the best performance of developed MPPT- P&O Fuzzy controller in tracking the MPP by achieving a better dynamic performance and high accuracy, compared with the use of the conventional MPPT- P&O under different atmospheric changes.