In the seismic design of secondary systems (SS) such as nonstructural components, the effect of torsional vibration of structural frames is not explicitly considered. Although torsional vibration may increase the inertia forces of SS, the degree of amplification and governing parameters have not been sufficiently clarified yet. In this paper, floor response spectra are investigated for single-story asymmetric buildings to understand the effect of torsion on SS. The results show that the maximum value of floor response spectrum becomes larger than that without the effect of torsion as the eccentricity ratio increases. But when the eccentricity ratio exceeds 0.1, the maximum value is almost constant at about 1.2 times larger than that without eccentricity.