Existing　studies　and　design　methods　for　the　progressive　collapse　(PC)　prevention　of　the　reinforced　concrete　(RC)　frame　structures　mainly　focus　on　the　vertical　PC　mode.　The　horizontal　PC　induced　by　the　failure　of　vertical　structural　members　could　lead　to　a　further　widespread　propagation　of　collapse.　But　the　research　on　the　horizontal　PC　of　RC　frame　structures　still　lacks　both　domestically　and　abroad.　An　asymmetric　planar　one-story　RC　frame　was　designed　and　the　static　collapse　test　was　conducted　to　analyze　the　mechanism　and　resistance　of　the　frame　to　resist　horizontal　PC.　Experimental　results　show　that　the　final　collapse　mode　of　the　frame　is　that　the　plastic　damage　formed　at　the　beam　ends　and　the　bottom　of　columns,　converting　the　statically　indeterminate　frame　into　a　planar　mechanism.　The　insufficient　horizontal　restraint　of　the　column　on　the　beams　and　slabs　leads　to　a　larger　vertical　displacement　of　the　frame　under　the　compressive　arch　mechanism,　which　consequently　reduces　the　contribution　of　the　compressive　forces　within　the　beams　and　slabs　to　the　collapse　resistance　of　the　frame.　The　collapse　resistance　of　the　frame　under　the　catenary　mechanism　is　mainly　determined　by　the　stiffness　and　strength　of　the　horizontal　restraint　of　the　column.　When　the　restraint　is　weak,　the　collapse　resistance　of　the　frame　under　the　catenary　mechanism　is　decreased　with　the　increase　of　the　vertical　displacement,　which　is　distinctly　opposite　to　the　results　of　the　existing　vertical　collapse　tests.　©　2016,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.