The　diamond-shaped　pylons　have　been　widely　used　in　engineering　practice,　due　to　their　cost　effectiveness　and　appealing　aesthetics,　particularly　for　the　cable-stayed　bridges　with　large　clearance.　However,　the　diamondshaped　pylons　have　both　inward　and　outward　inclinations,　which　may　result　in　complicated　seismic　behavior　when　subjected　to　earthquake　excitations.　To　this　end,　the　seismic　performance　of　a　typical　diamond-shaped　pylon　in　the　transverse　direction　is　investigated　in　this　paper.　A　reduced-scale　specimen　of　the　diamondshaped　pylon　was　tested　under　cyclic　quasi-static　load　to　evaluate　the　damage　patterns　and　the　hysteretic　responses.　The　numerical　models　of　the　diamond-shaped　pylon　were　developed　and　then　verified　against　the　experimental　results.　The　effects　of　the　geometric　configurations,　loading　protocols,　and　stiffness　of　crossbeam　on　the　seismic　performance　of　the　diamond-shaped　pylon　are　assessed　based　on　the　numerical　results　of　parametric　studies.　The　test　results　indicate　that　the　plastic　hinges　were　formed　at　the　diamond-shaped　pylon　legs　near　the　middle　intersections.　The　following　parametric　analyses　imply　that　the　failure　modes　and　damage　regions　would　be　changed　with　the　pylon　shapes,　stiffness　of　lower　and　middle　crossbeams,　and　loading　protocols.