This　paper　presents　an　experimental　study　on　the　seismic　behavior　of　polyethylene　naphthalate　(PEN)　fiber-reinforced　polymer　(FRP)-jacketed　circular　reinforced-concrete　(RC)　columns.　A　total　of　seven　specimens　were　tested　under　constant　axial　load　and　cyclic　lateral　load.　The　key　parameters　studied　were　the　thickness　(one,　two,　and　three　layers)　and　type　(PEN　FRP　and　CFRP)　of　FRP　jacket.　Test　results　indicated　that　the　control　column　failed　by　buckling　of　the　longitudinal　reinforcement　and　shortage　of　ductility,　while　concrete　spalling　and　bar　buckling　were　effectively　inhibited　by　the　application　of　external　FRP　jacket.　It　is　also　observed　that　PEN　FRP-jacketed　specimens　had　more　additional　strain　capacity　compared　with　CFRP-jacketed　specimens　at　the　final　condition.　The　additional　strain　capacity　can　serve　as　a　safety　reserve　for　structures　and　make　PEN　FRP　more　suitable　for　strengthening　large　or　noncircular　columns.　Furthermore,　it　is　found　that　1-ply　PEN　FRP　and　1-ply　CFRP　had　a　similar　strengthening　effect　and　thus　the　design　of　PEN　FRP-strengthened　column　can　simply　refer　to　the　design　method　of　CFRP-strengthened　columns　in　current　codes.　Different　FRP　thickness　and　types　had　marginal　impact　on　the　hysteretic　curves　of　the　specimens,　which　was　attributed　to　the　low　axial　load　ratio　(0.15)　and　high　slenderness　ratio　(5.25)　adopted　in　this　paper.　Finally,　based　on　a　cyclic　stress-strain　model　for　longitudinal　reinforcement,　including　buckling　effect,　developed　by　the　authors　in　a　previous　study,　the　test　columns　were　simulated　by　the　Open　System　for　Earthquake　Engineering　Simulation　(OpenSee)s　to　achieve　an　in-depth　understanding　of　the　experimental　findings　and　associated　strengthening　mechanisms.　Further　parametric　analyses　showed　that　considering　bar　buckling　played　a　significant　role　in　accurately　predicting　the　hysteretic　response　of　FRP-jacketed　columns.　　©　2023　American　Society　of　Civil　Engineers.