To investigate the spatial distribution of diatom valves in the surface sediment of Lake Kitaura, and to reveal the factors controlling diatom distribution,60 samples from surface sediments were analyzed. Diatom valve abundance was high (more than 4.0×10⁸ valves g^-1) in the area of fine grain sediment distribution, and low (less than 1.0×10⁸ valves g^-1) in the littoral zone. Diatom assemblages in the surface sediment were characterized by the predominance of planktonic taxa including Aulacoseira granulata, A. pusilla and Cyclostephanosd ubius. High abundances of tychoplanktonic taxa including Pseudostaurosira spp. (P. brevistriata and other species) and Staurosira spp. (S. construens var. construens, var. binodis, var. exigua, S. venter) were found in shallow areas in the northern and southern parts of the lake, and high abundances of benthic taxa including Navicula spp. and Cocconeis spp. at the northern end and littoral zone of the lake were also recorded. The diatom distributions in the surface sediment of the lake reflect the distribution of planktonic diatoms produced in the overlying lake water, tychoplanktonic diatoms occurred in the shallow area of the lake, and benthic diatoms transported from tributaries and the littoral zone of the lake.