Drug binding to plasma proteins is an inevitable process after the drug is distributed in the blood stream and it affects the pharmacokinetic and pharmacodynamic parameters of drugs. Since it changes the availability of the drug for the site of action and the free/unbounded fraction which is responsible for the biological effect, binding to plasma proteins is essential for the assessment of the strength and length of therapeutic action of drugs and in design of optimal dosage regimens. Phytoestrogens are natural plant compounds with non-steroidal structures which are functionally and structurally similar to estrogen and can bind to endogenous estrogen receptors. Due to the potentially positive and negative biological effects on the body, it is important to determine their bioavailability and proportion free/unbound fractions of phytoestrogens which can have a pharmacological effect. In this thesis binding of phytoestrogens to human serum albumin was examined by high performance liquid chromatography with chromatography column Chiralpak HSA. The assay showed high percentage of binding of phytoestrogens to human serum albumin (79-95%), which means that small fractions of phytoestrogens are free and available for biological effect. It was observed that small variations in substituents, such as methylation of the hydroxyl group or the presence of a glycoside, reflect on the binding to human serum albumin, or the retention time and the percentage of binding to HSA. Therefore, modifying the structure of phytoestrogens can affect their distribution and effect on the body.