The Gulf of Erdek is located in southwest Marmara Sea. Average and maximum depths are around 34 and 55 m, respectively. The study area is less polluted by pollutants of anthropogenic origin than the other gulfs (Izmit, Gemlik) in the Marmara Sea. The main source of fresh water and sediments in the gulf are the Gonen and Karabiga Rivers. These rivers, which receive pollution load from domestic, industries (ceramic factories and leather industry) and agricultural waste water from Gonen and Biga towns, drain into the Marmara Sea. In this study, distribution of historical heavy metal contamination derived from anthropogenic and/or natural origin was investigated in a 174-cm long core sediment collected from the mouth of the Gonen River at -16 m water depth. Heavy metal enrichment in the region was determined by analysing heavy metal (Cu, Pb, As, Zn, Cr and Co), grain size and total organic carbon (TOC) contents. According to the results obtained, average Cu, Pb, Zn, Cr and Co values in the core are 16, 68, 10, 26, 111 and 4 mg.kg(-1), respectively. The mean distribution of gravel, sand, silt and clay are 0.1, 1, 28.5 and 70.4%, respectively. TOC values range between 0.5 and 1.9%. Enrichment factor (EF) was calculated throughout the core to reveal the pollution history of the study area more clearly. Mean EF values through the vertical profile of the core are EF-Pb 12.2, EF-As 4.8, EF-Cr 3.3, EF-Zn 1.1, EF-Cu 0.9, and EF-Co 0.7. Based on Sutherland's (2000) enrichment factor contamination categories, core sediments were moderately contaminated with Cr and As, and contaminated significantly with Pb. The study area was not contaminated with Co, Cu and Zn. The EF-Pb, EF-As and EF-Cr values indicate that untreated anthropogenic waste water with agricultural and industrial origin (leather industry) was supplied into the gulf.