Polymeric materials are extremely important because of their wide range of applications, which is why they can be found all around us. For this very reason, large amounts of polymer waste are generated which, if not disposed of, can have a negative impact on people and the environment. One of the ways to dispose of polymer waste is mechanical recycling. Mechanical recycling has proven to be an effective way of processing thermoplastic polymers, enabling their reuse for the same or other purposes and reducing the total amount of polymer waste. Since mechanical recycling involving thermal processing can potentially cause some degree of material degradation, this study investigated whether the properties of high-density polyethylene (HDPE) change after multiple recycling cycles. Samples were analyzed after mechanical recycling using various methods, including thermal and spectroscopic techniques as well as mechanical testing, to determine whether the properties of this polymer material change (degrade) as a result of mechanical recycling. A total of 12 recycling cycles were performed and the HDPE samples were analyzed after the 3rd, 6th, 9th and 12th cycles as well as fresh HDPE. Fourier transform infrared spectroscopy (FTIR) was used to record the spectra of the samples, from which the carbonyl index (C.I.) was calculated to determine the degree of degradation. The thermal properties were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In addition, the melt flow rate (MFR) was determined and the mechanical properties of the samples were tested using a universal testing machine, which provided data on the tensile strength, elongation at break and elasticity of the tested samples. From the research results, it was concluded that multiple mechanical recycling has no significant negative effects on the chemical structure and properties of high-density polyethylene, which would limit the use of recycled HDPE, i.e. mechanical recycling is an effective method of HDPE recycling.