Dermatan sulphate (DS) belongs to the group of glycosaminoglycan (GAG) polysaccharides. DS is present in various tissues in higher organisms, e.g. in skin, blood vessels or lungs and plays important roles in various processes. The proper knowledge of the DS chemical structure is therefore essential for understanding biological role of this GAG. The main contribution to the investigation of DS solution properties and formation of their intermolecular complexes with proteins are methods of theoretical chemistry, together with high-resolution NMR spectroscopy. In the present contribution, the results of calculations of molecular geometry of dermatan sulphate by density functional theory (DFT) are discussed and compared with experimental spectroscopic data. The data showed that the positions of sulphate groups at the pyranose rings significantly influenced the molecular structure of the investigated DS tetrasaccharide. The computed data also revealed that formation of a complex hydrogen bond network and strong ionic interactions influence the first hydration shell and plays important role in shaping the three-dimensional structure of DS tetrasaccharide.