Parasitic effects in a lumped-element multilayer LC resonator are analyzed with an equivalent circuit. An optimization technique is proposed. With this technique, undesired influences of parasitic effects may be reduced. Meanwhile, some of the parasitic effects may be used for the size-reduction and performance improvement. A lumped-element multilayer LC resonator is used for demonstration. The optimized resonator outperforms the resonator before optimization in both performance and size. A multilayer filter composed of four LC resonators is used for verification. The measurement results agree very well with circuit results. The measured parasitic resonances are higher than the third harmonic frequency. These facts show the effectiveness of the proposed technique.