Focusing　on　the　combined　effects　of　the　horizontal　reinforcement　ratio　and　the　structural　size　on　the　seismic　performance　of　BFRP　reinforced　concrete　(BFRP-RC)　shear　walls,　the　present　study　experimented　on　six　shear　walls　with　different　structural　sizes　up　to　1800　mm　×　1800　mm　×　240　mm　(length　×　height　×　thickness)　having　various　horizontal　reinforcement　ratios　of　0.25%　and　0.50%.　From　the　experiment,　it　is　concluded　that:　(1)　the　failure　modes　of　the　specimens　with　horizontal　reinforcement　ratios　of　0.25%　and　0.50%　are　mainly　shear　failure　and　compressive-shear　failure,　respectively.　(2)　When　the　length　of　the　specimen　increases　from　600　mm　to　1800　mm,　the　nominal　cracking,　elastic　and　shear　strength　of　shear　walls　with　the　horizontal　reinforcement　ratio　of　0.25%　(resp.　0.50%)　decreases　by　66%　(resp.　59%),　30%　(resp.　29%)　and　28%　(resp.　24%),　respectively.　The　results　demonstrate　that　the　size　effect　on　the　BFRP-RC　shear　wall　is　significant.　Meanwhile,　the　ductility　coefficients　decreased　by　19%　(resp.　22%),　and　energy　dissipation　coefficients　decreased　by　39%　(resp.　18%).　(3)　When　the　horizontal　reinforcement　ratio　increases　from　0.25%　to　0.50%,　the　nominal　shear　strength　of　specimens　with　lengths　of　600　mm,　1200　mm　and　1800　mm　increases　by　14%,　15%　and　19%.　It　is　worth　noting　that　the　size　effect　is　significantly　suppressed　with　the　increase　of　horizontal　reinforcement　ratios.　Besides,　the　good　consistency　found　between　the　experiments　and　the　size　effect　law　proposed　by　Jin　et　al.　allows　the　validation　of　the　accuracy　and　rationality　of　the　size　effect　law.　©　2023　Elsevier　Ltd