In order to clarify the mechanism of fucoidan transport, we developed the chromatographic determination method. A size-exclusion chromatography (SEC) method for the determination of Okinawa-fucoidan using Develosil 300 Diol-5 (60×8.0mm I.D., 30nm pore-diameter) with the eluent containing 1% non-ionic detergent is developed. Determination range (UV at 210nm) is from 0 to 100ng of fucoidan with the linear calibration line inserting to zero. A transport activity of fucoidan is demonstrated by using Caco-2 cells (model of gut transport system); i.e., the initial transport velocity 12nmol/h/mg of protein (25-fold slower rate as compared to a bacterial l-alanine active-transport activity 300nmol/h/mg of protein) is found to occur. Since this fucoidan transport is inhibited by 10mM sodium azide (respiration inhibitor) and 0.05mM FCCP (uncoupler), this transport by Caco-2 cells is found to be an active one requiring energy-source. On the other hand, colchicine (inhibitor of phagocytosis/pinocytosis) and mannitol (putative competitive-inhibitor of tight-junction transport) cannot inhibit the fucoidan transport at all. We firstly report that the active transport occurs for such a high molecular-weight sulphated-polyfucose of fucoidan in vitro using Caco-2 cells.