The　limit　of　height-width　ratio　of　base-isolated　structure　with　rubber　bearings　is　investigated.　Two　sufficient　conditions　that　could　keep　the　base-isolated　structure　from　overturning　during　strong　earthquake　are　considered.　One　is　that　rubber　bearings　should　not　be　subjected　to　tensile　stress,　and　the　other　is　that　the　compressive　stress　in　rubber　bearings　should　not　exceed　the　allowable　value.　The　derivation　of　limit　ratio　formulas　are　performed　and　the　results　are　presented　corresponding　to　different　building　categories,　earthquake　fortification　intensities,　site　classifications,　and　damping　ratios　of　isolated　story.　In　the　formulas　for　the　axial　force　in　rubber　bearings,　vertical　seismic　action　and　the　most　unfavorable　load　combinations　are　considered.　It　is　found　that,　the　limit　ratio　increases　with　the　isolation　period　when　it　is　confined　by　the　first　sufficient　condition,　and　decreases　when　confined　by　the　second　one.　So　there　exists　a　critical　period,　at　which,　the　limit　ratio　reaches　its　maximum　value.　It　is　also　found　that　there　exists　a　maximum　isolation　period,　at　which,　the　limit　ratio　is　zero　or　the　horizontal　displacement　of　the　rubber　bearing　exceeds　the　allowable　value.　By　comparing　the　isolation　period　with　the　critical　and　maximum　periods,　the　limit　ratio　can　be　obtained　by　using　the　corresponding　formulas.　In　conformity　to　the　principle　of　simplicity　and　safety,　the　calculated　limit　ratios　were　summarized　to　obtain　the　suggested　values.　The　limit　height　of　base-isolated　structures　are　also　calculated　by　using　the　period　formulas　of　non-isolated　structures　as　suggested　in　the　design　code.