This study deals with an experimental investigation on the suppression of flow-induced vibrations of two circular cylinders in tandem arrangement. In this study, the tripping rods which are attached in symmetry about the stagnation point of circular cylinders are used to suppress the flow-induced vibrations in cross-flow vibration. The response characteristics on elastically supported two circular cylinders are examined by a free vibration test when the spacing ratio L/D (L is the gap spacing between two cylinders, D is the diameter of cylinder) and the position of the tripping rods are variously changed. Also, the behavior of the shear layers separated from the two circular cylinders are investigated on the basis of the visualized flow patterns. The main findings are that (i) the effect of suppression for flow-induced vibrations of two circular cylinders terrifically changes by the installing angle of the tripping rods on the cylinder surface, (ii) when the tripping rods are installed at 20 and 30 degrees from stagnation point, the flow-induced vibrations of the two cylinders are almost suppressed at which less than the critical spacing L/D=2.7, (iii) when the tripping rods are installed at the position beyond 40 degrees, the flow-induced vibrations of the two cylinders are considerably larger than those of the cylinders without the tripping rods.