This paper presents a five-level inverter which is used as a three-phase four leg shunt active power filter, taking advantages of the multilevel inverter such as low harmonic distortion and reduced switching losses. It is used to suppress harmonic current, compensate reactive power and neutral line current and balance the load currents under unbalanced non-linear load and distorted voltage conditions. The active power filter control is essentially based on the use of self tuning filters for the reference current generation and a fuzzy logic current controller. This study is divided in two parts. The first one deals with the harmonic isolator which generates the harmonic reference currents. The second part focuses on the generation of the switching pattern of the inverter by using a fuzzy logic controller applied and extended to a four leg five level shunt active power filter. The MATLAB Fuzzy Logic Toolbox is used for implementing the fuzzy logic control algorithm. The performance of the proposed shunt active power filter controller is found considerably effective and adequate to compensate harmonics, reactive power and neutral current and balance load currents under distorted voltage conditions.