In the seismic control of bridge structures in the transverse bridge direction, viscous dampers and steel dampers are seismic control devices with high reliability, and both have been initially applied in several bridge projects. In this paper, a comparative study of the two types of damping devices was carried out in terms of their ope-rating principles, constructional realization form, mechanical behaviour and seismic damping effects. The mechanical behaviour of the viscous dampers was compared with that of the steel dampers in the literature. As to their seismic damping effects, the difference in response between the two devices and the bridge structure under the excitation of 28 seismic waves was discussed by taking a three-tower cable-stayed bridge as the example. Based on one of the 28 seismic waves, the causes of this phenomenon was analyzed from the perspective of energy. The results show that the different damping devices have different energy dissipation mechanisms, resulting in different dynamic responses, but the seismic response shows no significant change; the viscous dampers are more effective than the steel dampers in controlling the bridge cross-bridge ground vibration at the transition and auxiliary piers under Class I site conditions.