We measured phosphate benthic fluxes and conducted phosphate adsorption experiments in order to find out the effects of adsorption on phosphate benthic fluxes in the intertidal sediments of Keunso Bay during summer and winter. Organic carbon contents showed little variation with season at St. S1, but noticeable changes were observed at St. S2, which were three times higher in winter than in summer. The higher organic carbon contents in winter resulted from the bloom of benthic algae in surface sediments. Pore water phosphate concentrations were much higher in summer than in winter. The higher phosphate concentration in summer was probably due to the faster remineralization rate of organic matter in summer. At St. S1, benthic fluxes of phosphate showed a negative value in summer and a positive value in winter. However, St. S2 had a negative benthic flux both in summer and winter. The negative benthic flux was ascribed to the phosphate adsorption on iron oxides in surface sediments. The equilibrium concentrations of phosphate obtained from the adsorption experiment were three times higher at St. S1 than at St. S2. The relatively high adsorption coefficient and low equilibrium concentration indicated that phosphate was strongly adsorbed on the surface sediments of Keunso Bay. The strong adsorption affinity significantly reduced benthic fluxes of phosphate in the intertidal sediments.