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This paper presents two new methodologies for optimal placement of distributed generation (DG) in a locational marginal price (LMP) based on wholesale electricity market. A Gravitational Search Algorithm (GSA) is proposed for simultaneous power quality improvement, optimal placement and sizing of fixed capacitor banks in radial distribution networks with nonlinear loads and distributed generation (DG) imposing voltagecurrent harmonics. In distribution systems, nonlinear loads and DGs are often considered as harmonic sources. For optimizing capacitor placement and sizing in the distribution system, objective function includes the cost of power losses, energy losses and capacitor banks. In this study, new fitness function is used to solve the constrained optimization problem with discrete variables. Simulation results for modified 12 IEEE are presented and solutions for the proposed method are compared with previous methods. The proposed methods complyengineering aspects of system operation and economic aspects of market operation and act as good indicators for the placement of DG, especially in a market environment. In order to provide a scenario for DGs available, several cost characteristics are assumed. For each DG cost characteristic, an optimal placement and size are identified for each of the objectives. Results show that proposed GSA method could be effectively used for optimal capacitor placement and sizing in distorted distribution systems.