A　modified　suction　caisson　(MSC),　which　was　reported　by　the　authors　of　this　paper　previously,　comprises　an　external　short-skirted　structure　that　is　added　to　a　regular　suction　caisson　(RSC).　It　has　been　proved　that　MSCs　can　improve　the　lateral　bearing　capacity　and　limit　the　deflection　of　the　caisson　compared　with　RSCs.　A　series　of　model　tests　were　conducted　to　investigate　responses　of　MSCs　subject　to　uplift　loading　in　saturated　sand.　The　effects　of　external　skirt　dimensions　on　the　uplift　bearing　capacity　of　MSCs　were　considered.　In　addition,　the　influences　of　the　sealed　top　lid　of　the　skirted　structure　on　the　uplift　bearing　capacity　and　the　resulting　passive　suction　of　MSCs　were　also　studied.　It　was　found　that　the　uplift　bearing　capacities　of　MSCs　are　1.4–1.7　times　that　of　RSCs.　Moreover,　test　results　in　serviceable　conditions　show　that　the　sealed　external　skirted　structure　of　perspex-made　suction　caissons　significantly　contributed　to　the　uplift　bearing　capacity　as　a　result　of　passive　suction.　©　2017,　Tianjin　University　and　Springer-Verlag　GmbH　Germany.