The　hysteretic　capacity　of　reinforced　concrete　(RC)　structures　depends　to　a　large　extent　on　the　hysteretic　behavior　of　steel　bar　to　sustain　many　cycles　of　high　plastic　deformations　without　obvious　degradation　of　strength　and　stiffness.　It　is　important　to　develop　an　accurate　and　computationally　efficient　model　of　steel　bar　in　the　nonlinear　response　analysis　of　RC　structures　subjected　to　cyclic　loads.　The　high　strength　and　ultra-high-strength　(UHS,　yield　strength　above　1000　MPa)　steel　bars　are　becoming　more　and　more　popular　in　concrete　construction,　which　is　beneficial　for　materials　saving　and　reduction　of　steel　bar　congestion.　In　order　to　investigate　the　cyclic　behaviors　of　UHS　steel　bars　and　to　propose　a　hysteretic　model　for　this　kind　of　steel　bars　including　buckling,　a　total　of　54　specimens　with　nine　slenderness　ratios　were　carried　out　under　compressive　and　cyclic　loadings.　The　modified　stress-strain　curve　model　of　UHS　steel　bars　with　different　slenderness　ratio　was　developed　based　on　the　experimental　data,　which　can　take　buckling　and　fatigue-induced　reduction　of　stress　into　account.　This　study　offers　a　solid　database　for　researches　on　the　mechanical　properties　of　UHS　steel　bars.　And　the　proposed　empirical　model　can　easily　be　implemented　in　the　finite　element　analysis　of　RC　elements　with　UHS　steel　bars　under　cyclic　loadings.