Hyaluronic acid (HA) is an essential component of the bone extracellular matrix (ECM) as it maintains the viscoelasticity of the ECM and plays a vital role in many biological processes - controls cell-cell and cell-ECM interactions, regulates cell adhesion, proliferation and differentiation. Additionally, as HA has excellent biocompatibility and is completely biodegradable in vivo, it is an attractive material for the preparation of hydrogels with the desired morphology and bioactivity [1]. However, HA hydrogels lack of mechanical stability and are rapidly degraded in vivo by such enzymes as hyaluronidases. To overcome these shortcomings, HA hydrogels can be modified with an inorganic component of natural bone - calcium phosphate (CaP), thus providing bone-mimetic microenvironment, promoting the bone regeneration and increasing stability of hydrogels [2]. The aim of the current study was to evaluate the influence of inorganic phase (CaP) addition on molecular structure, microstructure, gel fraction and swelling behavior of HA hydrogels. Two different approaches were used for HA/CaP composite preparation – in situ CaP synthesis in HA solution and mechanical mixing of CaP and HA. In both prepared composite systems inorganic/organic phase ratio was kept constant.