Bone cements based on poly methyl-methacrylate (PMMA) are among the most widely used polymer composites in orthopaedic surgery. They play a key role in fixing the endoprosthesis with the bone, and, as such, are the weakest link in total joint replacement (TJR) surgeries. A fast, premature decrease in the mechanical properties of PMMA in an aggressive environment, such as the human body, can lead to TJR loosening, which results in the necessity for revision surgery. In recent years researchers have undertaken studies on the possibility of enhancing the mechanical properties of PMMA by adding various admixtures in different concentrations. In this study we present the results of the mechanical properties of samples made of the commercially available and widely used in orthopaedic surgery PMMA bone cement (Palamed® Heraeus) that was admixed with glassy carbon (GC) using different concentrations. All samples were subjected to compression testing. Compression reflects the load mechanism acting on PMMA in the human body after TJR implantation. The study involved comparing selected mechanical parameters of both samples prepared according to the manufacturer’s instructions and samples prepared with the addition of GC with grain sizes of 0.4–12 μm and 20–50 μm. Although this material can potentially increase the mechanical strength of PMMA, serious contamination with GC can lead to PMMA polymerization impairment due to the thermal properties of GC and, consequently, affect the mechanical properties of PMMA. GC was added in the following w/w concentrations: 1, 2, 3, 5, 8 and 10 %. Results revealed a significant decrease in the compression strength of PMMA following the addition of 20–50 μm GC, which resulted from the disturbances in standard polymerization process conditions (time and temperature). Interestingly, the addition of 0.4–12 μm GC did not affect significantly the compressive strength of the material in the tested range of concentration.