We have developed a new type of fluidized-bed called a circulating fluidized-bed adsorber (CFBA) that brings adsorbent particles into contact with a large quantity of water at high efficiency. In the present study, effects of outer scale and internal structure of the CFBA on the uranium uptake from natural seawater were investigated, and some improvements in the adsorption ability of the CFBA were achieved. By improving the internal structure of the CFBA, the total amount of uranium recovered from natural seawater became 1.6 times larger than that in an adsorber developed at the beginning of the study. The uranium recovery efficiency of the CFBA was compared with that of a conventional fluidized-bed adsorber. The amount of uranium adsorbed per unit volume of the CFBA was evaluated to be 20 % larger than that of the fluidized-bed adsorber. Operational stability of the CFBA was examined for eighteen days. In spite of using unfiltered seawater, clogging did not occur during the adsorption period. The CFBA ran very stably.