Millions of PET bottle wastes occur in the world. These wastes are used as additives in different ways in solid form in many areas However, using PET bottle waste in solid form limits their usability in some areas (geotechnics, building materials). In this study, the effect of liquefied PET bottle waste(LPBW) on some physical and mechanical properties of fine-grained soil was investigated. For this purpose, Atterberg Limits (wL, wP) and unconfined compressive strength tests were carried out with the samples prepared by adding different ratios (5%, 10%, 15% and 20%) to the mixing liquid of the fine-grained soil, which was turned into viscous liquid PET bottle wastes. From the results of the experiments carried out in the laboratory, it has been shown that adding liquefied PET bottle waste material to the mixing water ata rate of up to 5% increases the unconfined compressive strength. In addition, it was determined that the workability of fine grained soils increased with the increase of liquefied PET bottle waste added to the mixing water.