Controlling of undesired circulation of power flows in the de-regulated power systems is one of the most important problems for a power system operator. Although he/she may have some tools such as phase-shifting transformers to take remedial actions they may not be sufficient for system-wide actions. The problem gains more importance when an interconnected power transmission system is operated at or close to its power-carrying limits. Thus, the problem of the prevention and/or control of loop flows (also called unscheduled power flow) need be solved efficiently and fast. In this paper, a fuzzy set theory based procedure using genetic algorithm is proposed for the solution of this problem. The constraints and objectives are handled in a fuzzy environment and the resulting optimization problem is solved using genetic algorithm. The proposed method is applied to the IEEE 30 and 118 bus test systems and the results are presented. Copyright (C) 2010 Praise Worthy Prize S.r.l. - All rights reserved.