The August 17, 1999 Marmara (Turkey) earthquake of magnitude (M-w = 7.4) struck the Marmara and Sakarya provinces in north-western part of Turkey. The earthquake caused substantial casualties and severe damages to structures. Adapazari in Sakarya province clearly suffered the worst damage due to geotechnical effects since the city is located over young riverbed sediments with soft and liquefiable silts and sands. Structures located on the surface of the liquefiable soils severely settled or tilted owing to the loss of bearing capacity of the soil. In this study, an assessment of liquefaction potential in Adapazari city during 17 August, 1999 Marmara earthquake is investigated based on Standard Penetration Test (SPT) measurements available. The evaluation of liquefaction potential has been analyzed by four well-known methods namely the Simplified Procedure, Tokimatsu-Yoshimi, Seed-De Alba method and the Japan Road Association. A computer program developed originally by the writers which achieves the computations for liquefaction susceptibility. The results of assessment based on the Simplified Procedure were generally consistent with the actual performance of the ground investigation.