In 1984 the authers produced a torsional earthquake response testing system in which actuators were linked to personal computer (personal computer-actuator on-line system) by way of reproducing seismic behavior of structures with eccentricity. Using this system the authors have performed experiments on torsional earth-quake response of reinforced concrete structures with eccentricity. In this paper the outline of the personal computer-actuator on-line system and the experimental results on torsional earthquake response of coupled reinforced concrete frames, where eccentricity is varied, are re-ported. According to this experiment a large difference can be seen in torsional earthquake response of coupled reinforced concrete frames which have the same stiffness and ultimate strength with varying eccentricity.