The power quality in distribution systems becomes deteriorated due to an increase in nonlinear loads. This paper presents a new method, based on interactive multiobjective nonlinear programming (MONLP), using genetic algorithms (GAs) to study passive filter planning. The short-circuit capacity of the point of common coupling (PCC) and the individual bus loads are modeled with the fuzzy sets. The harmonic voltages and the filter cost are minimized while satisfying the harmonic standard and harmonic power flow equations with the harmonic Y-matrix. An 18-bus system is used as a test system for showing the applicability of the proposed method.