In this study, the effect of sample preparation method on the liquid limit and plastic limit values was examined. For this purpose, the liquid limit and plastic limit values of the samples, which have been determined by dry preparation method defined in ASTM D 4318-00 (standard method) and the method followed by some laboratories in Turkey (non-standard method) were compared. In the study, 30 natural soil samples with a liquid limit values ranging between 30% and 90% taken from various locations of Turkey were used. The liquid limit tests were carried out by both Casagrande and cone penetration methods. Test results indicate that the liquid limit values of the samples prepared by standard method are greater than those of the samples prepared by the non-standard method, up to 10% in the Casagrande method and up to 8% in the cone penetration method. The plastic limit values of the samples which were prepared by the standard method are greater than those of the samples prepared by the non-standard method up to 3%. It was also observed that the soil type of the some samples according to USCS may be altered due to differences of the sample preparation method.