Since March, 1957, the authors have been engaged in studies of floating seaweeds with some reference to living and cast up materials. For collecting the floating seaweeds materials a rectangular scoop-net being ca. 3x 3.7 m in size was used. The surveys were carried out twice a month in general, on the facilities of the Fishery Research Laboratory of Kyushu University. Though the survey area was limited (Fig. 1), annual results are summarized as follows : 1) T h ere was no significant difference in species among three sorts of materials : floating, cast up and living fucaceous algae (Tab. 1). Because the area having such a flora may spread widely to northern Kyushu, the origin of the floating seaweeds can not be supposed from this examination. But the fact of an unexpectedly little amount in Eusargassurn species, characteristic Sargassums of warmer seas, shows that the floating seaweeds in this area are not of southern Kyushu origin. 2) From the quantitative composition of common species in floating seaweeds a remarkable seasonal vicissitude in each species is observed (Fig. 2). 3) The amount of floating seasonal could not be determined precisely, b ut it seems more abundant from April to May, and less in autumn. It is due to the size of seaweeds, i. e. Sarg. horneri, one of the floating seaweeds with a spring fruiting period, often reaches over several metres in spring, whereas Sarg. ringgoldianum, a representative of the autumn materials, hardly grows over one metre even in its fruiting period of autumn. In addition, the weather condition is also another cause in making weeds float from their substrata. Without hard wind or strong action of sea water they would not be able to get free from their substrata, excepting they decay in the basal parts in afterlife.