Wines contain various biologically active polyphenolic compounds that are belived to have numerous beneficial effects on human health. The polyphenolic profile of wines is often used to evaluate their quality and authenticity. In this doctoral thesis, a comparative chemical characterization of polyphenols was performed in twenty-five commercial red and white wines produced in different Croatian wine-growing regions from eight black and nine white grape varieties. For this purpose, a method of high-performance liquid chromatography (HPLC-DAD) with direct injection of wine was developed and validated. Twentyfour polyphenolic components of the wines were studied and classified into five groups based on their structure: phenolic acids, flavan-3-ols, anthocyanins, flavonoids and stilbenes. Black wines contained significantly higher concentrations of polyphenols than white wines, and a great variability in their composition was found. Wines produced from the native Croatian varieties Plavac mali and Babić were characterized by their specific polyphenolic composition and content. Multivariate analysis was used to determine similarities and differences in the polyphenolic profiles of Croatian monovarietal wines and to identify important differentiators. The main representatives of polyphenolic components, which were significantly present in the studied wines, showed strong antioxidant activity and the ability to inhibit the activity of Src tyrosine kinase, α-glucosidase and acetylcholinesterase enzymes. The conducted research provided new insights into the polyphenolic profiles of Croatian wines, thus contributing to their varietal differentiation, authentication and quality control. It was found that the analyzed red wines, especially those obtained from Croatian autochthonous red grape varieties, are a valuable source of polyphenols with strong antioxidant properties and the ability to inhibit enzymes that are important therapeutic targets in the prevention and treatment of some chronic diseases associated with aging.