Power-bus resonance of printed circuit board (PCB) causes propagation of electromagnetic noise and detraction of power integrity. For suppressing the power-bus resonance, the following two aspects are important: suppression of power-bus resonances focusing only on each specific resonance; reduction of the resonant energy stored between the power and ground planes. In this paper, we propose a lossy resonator filter consisting of an open stub covered with a magnetic thin film. This paper first explains the concepts of the proposed filter, especially focusing on the impedance characteristics, and then demonstrates that the proposed filter suppress power-bus resonances effectively by full-wave simulation.