Poly methyl-methacrylate (PMMA) is one of the most widely used polymer composite materials in orthopaedic and trauma surgery. However, this material can change its mechanical properties when exposed to the highly aggressive environment of the human body, which may result in joint implant loosening and thus in a need for revision surgery. Therefore, in recent years, numerous researchers have investigated the effect of adding various particles to PMMA in order to obtain a composite bone cement with enhanced mechanical properties. In our study, we examined the effect of adding different grain sizes of hydroxyapatite (HA) to the commercially available PMMA (Palamed, Heraeus) on the mechanical properties of the fabricated PMMA/HA bone cement composite. Samples were subjected to compressive loading, as this type of load reflects typical conditions in the human body after joint prosthesis implantation. Hydroxyapatite of two different grain sizes was used: 5 µm (HA5) and 10 µm (HA10). Being a naturally occurring bone mineral, hydroxyapatite can improve the biocompatibility of bone cements, which would prolong the total joint replacement (TJR) survival rate. However, when added to PMMA, HA can affect its mechanical properties. In this study, the effects of adding HA was added in 0, 1, 2, 3, 5, 8, 10 % of dry mass were analysed. Obtained results demonstrated that only the addition of 2 % HA had a significant impact on the mechanical properties of PMMA. The other percentage concentrations had no effect on PMMA properties.