In this paper a procedure for sidelobe suppression in the frequency response of a MIM (metal-insulator-metal) plasmonic filter is presented. Using the calculated effective refractive index for various values of the width of dielectric core and Bragg condition, the structural profile of primary filter is obtained. The frequency response for the transmission coefficient of the MIM plasmonic filter is derived by TRC-LOD-FDTD method. The variation in the frequency response of the filter due to changes in the structural parameters is studied. Finally, the usage of Gaussian, sinusoidal and linear types of gratings in suppressing the sidelobes and their effects on the stop-band bandwidth of the MIM plasmonic filter is investigated.