A study of the washing process for recycling HDPE (High-Density Polyethylene) materials was reported. The materials used are taken from one source and the same type, namely white, used packaging bottles. The study begins with washing the HDPE waste through a series of washing processes, using NaOH 48% solution and followed by water rinsing. In this study, samples of used HDPE bottles with the same color were washed at two different temperatures, at 27°C (room temperature) and 50°C, for 30 minutes. Characterization of the washing water was carried out to measure pH, conductivity, and alkalinity. The results show that the difference in washing water temperature does not significantly affect the resulting pH, while the conductivity of washing water at room temperature was found to reach lower conductivity with fewer rinsing process than washing water with a temperature of 50°C. The 0% alkalinity is found in the second and fifth rinse for washing water at the temperature of 27°C and 50°C, respectively. Before and after the washing procedure, the samples were subjected to a mechanical test using the Leeb Hardness Tester to see whether the washing process affected the sample's mechanical properties. The result for Leeb Hardness Tester shows an increasing value from 540.4 HL for the sample before treatment to 577.8 HL and 586.8 HL after treatment with a temperature range of 27°C and 50°C, respectively. Thermal analysis was carried out by DSC (Differential Scanning Calorimetry) and TGA (Thermogravimetric Analysis). The curve of DSC results showed no significant difference in material properties after five times the washing process. Characterization of the sample was also carried out by FTIR (Fourier Transform Infrared Spectroscopy) in the range from 4000 to 550cm-1 to identify the effect of heat on the polymer chains. Both the treated and untreated samples showed the same results.