Bi-axial　quasi-static　tests　on　14　reinforced　concrete　thin-walled　piers　with　rectangular　hollow　cross-sections　were　carried　out.　The　bidirectional　seismic　properties,　including　load-displacement　hysteresis　curve,　skeleton　curve,　displacement　ductility,　hysteretic　energy　and　ultimate　curvature,　were　discussed　in　consideration　of　the　influence　of　slenderness　ration,　axial-load　ratio　and　ratio　of　reinforcements.　Results　show　that　flexural　failure　is　the　main　failure　mode　of　the　piers,　the　damage　area　of　short　piers　focuses　on　the　bottom　area　while　the　damage　area　of　high　piers　moves　upward　obviously.　The　piers　with　bigger　slenderness　ratio　and　smaller　axial-load　ratio　have　more　full　hysteresis　curves　and　bigger　deformation　capacity,　which　reveals　excellent　seismic　performance.　As　the　slenderness　ratio　ranges　from　6.9　to　13.1,　the　displacement　ductility　of　the　pier　decreases　as　slenderness　ratio　increases,　but　the　displacement　ductility　of　the　pier　with　a　slenderness　ratio　of　16.3　is　obviously　big.　The　piers　with　slenderness　ratio　bigger　than　13.1　have　big　plastic　damage　area,　but　their　ultimate　curvature　declines　obviously.