Seismic　response　of　the　bridge　piers　to　horizontal　ground　motion　is　investigated　for　various　cases:　rigid　and　flexible　foundation,　without　and　with　water.　The　purpose　of　this　study　is　to　evaluate　the　fluid-structure　interaction　and　soil-structure　interaction　effects　on　the　seismic　response　of　the　circular　cylinders.　The　fluid-structure　interaction　is　simulated　by　added　mass　approach　and　the　soil　supporting　the　massless　foundation　modeled　as　spring-damper　elements　is　used　to　simulate　soil-structure　interaction.　The　focus　is　placed　on　gauging　the　significance　of　physical　parameters　that　affects　the　seismic　response　of　the　piers.　An　equivalent　SDOF　system　that　the　pier　is　simplified　as　a　single　lumped-mass　model　is　utilized　to　investigate　the　effects　fluid-structure-soil　interaction　on　dynamic　properties　of　the　piers.　The　results　indicate　that　the　effects　of　fluid-structure　interaction　are　more　significant　for　slender　piers　and　cause　an　increase　in　deflections,　shears　and　periods,　and　the　effects　of　soil　structure　interaction　are　more　significant　for　squat　piers　and　cause　a　decrease　in　deflections,　shears　and　an　increase　in　periods.　The　study　shows　that　the　fluid-structure　interaction　is　more　important　for　hard　soil　while　the　soil-structure　interaction　is　more　important　for　soft　soil　in　fluid-pier-soil　system.