Tributyltin (TBT) is used as effective antifouling agents in boat paints and has been found to be present in marine and freshwaters ecosystem at concentrations exceeding acute and chronic toxicity levels. In the present study, horizontal and vertical TBT distributions in the sediment of Hakata Bay, Japan, have been investigated. Basic properties of the sediment such as clay mineralogy, particle size and organic matter content were also determined, and their relations with TBT concentrations in the sediment were discussed, focusing on organic matter. Sediments in the study sites consist mostly of clay soil with clay fraction of 21 % to 35 %, and major clay minerals in the sediments were smectite, followed by vermiculite, illite, and kaolinite. TBT concentration in overlying water ranged from 13 to 94 ng·L⁻¹ at locations within the harbor, and from 13 to 32 ng·L⁻¹ at locations outside of the harbor. TBT concentration in top 3 cm sediment varied from 0.018 to 1.101 mg·kg⁻¹. Sorption coefficient was in a range of 1.03 to 5.7×10³ (L kg⁻¹) for sediments at most stations, and on the order of 10⁴ for sediments with higher organic matter content. The organic matter content and TBT concentration in sediments changed with depth in a similar pattern at all stations. The organic matter decreased with depth up to 12 cm and was almost constant below 12 cm. TBT concentrations appeared to be higher at depth above 12 cm than below 12 cm. A positive correlation was observed between TBT concentration and organic matter content for all core samples data. According to other researchers, an increase in TBT concentration due to increase in organic matter appears to be the results of sorption of TBT⁺ on negatively charged surfaces of organic matter as well as hydrophobic sorption of TBT compounds on organic matter.