Preconsolidation pressure is a very important parameter which affects the stress history and the behaviour of the cohesive soils in geotechnical engineering. The preconsolidation pressure is usually determined using the graphical methods. In this research, the clay samples were preloaded in slurry consolidoemeter and Rowe cell and some samples were prepared as remoulded ones in laboratory conditions. Some samples taken from the Rowe cell and remoulded samples were prepared under various isotropic and anisotropic stress conditions in triaxial test cell. After preparation of samples, oedometer tests were conducted on all samples. The preconsolidation pressure values determined by implementing various methods given in geotechnical literature, i.e. Casagrande, Schmertmann, Janbu, Butterfield, Tavenas, Burmister, Old and Van Zelst methods were examined in terms of regression analyses. Finally a new preconsolidation determination method based on generally Tavenas method has been suggested.