This　paper　presents　results　form　a　series　of　model　tests　performed　to　study　penetration　behaviour　of　the　modified　suction　caisson　(MSC)　in　clay.　By　comparing　with　the　regular　suction　caisson　as　a　reference,　features　of　MSCs　penetration　were　discovered.　The　phenomenon　of　MSCs　penetration,　the　relationships　between　time,　penetration　depth,　velocity　and　the　required　suction　were　discussed　in　order　to　obtain　the　change　in　the　penetration　resistance.　When　the　external　skirt　touches　the　mudline,　the　tip　resistance　and　the　shaft　frictional　force　of　the　MSC　increases　sharply.　Expressions　of　estimating　the　resistance　to　penetrating　the　MSC　was　proposed.　It　was　found　that　when　the　MSC　is　penetrated　into　clay　with　low　shear　strength,　the　penetration　resistance　obtained　by　using　the　proposed　method　is　smaller　than　the　model　test　result,　indicating　that　the　disturbance　of　the　clay　induced　by　the　suction-assisted　installation　cannot　be　ignored.