In the Nakdong River delta, the depositional environment is slightly different in every locality. An attempt was made to conduct a geotechnical characterization of clay in the floodplain of the delta area, where a series of field and laboratory tests was executed at five sites. The results indicate that variations in the slope of cone resistance change with depth are utilized to stratify the deposits and to extend a paleoenvironmental profile that has been investigated at a neighboring site. Some of the index properties and the compression index appear to correlate with the depositional environment, so that they have a well-defined trend with depth irrespective of location and empirical formulas may be developed between them. However, on the top 10 m layer deposited during regression, several properties are different in the tested sites. The ratio of the field vane strength to the effective overburden stress shows a poor correlation with water content, indicating no relationship with the plasticity index. The in-situ void index Iv0 shows that clays of the Tidal Flat (TF) and Inner Shelf (IS) units are more structured than other normally consolidated clays, whereas that of the Shallow Marine (SM) unit, which is overconsolidated, is not. The sensitivity (St), ranging from 5 to 9 at a location, vary in a manner similar to a well-defined trend of the properties. Based on the Iv0, recompression, and Cc-e0-St relation, the clay is moderately or highly structured but weakly bonded, where Cc is compression index and e0 is initial void ratio.