The study of the selective solvation of hydroxycinnamic acids (para-coumaric, caffeic) by a polar cosolvent (acetone, methanol) in supercritical carbon dioxide at T = 328 K, p = 0.772 g/cm(3) has been carried out using the molecular dynamics and quantum-chemical calculations. It has been shown that the selective solvation of the solute occurs by the formation of hydrogen-bonded complexes with a cosolvent. The formation of hydrogen bonded complexes with two or more cosolvent molecules is most likely in methanol-modified supercritical carbon dioxide even at a low concentration of the methanol, whereas the formation of a complex with one cosolvent molecule is preferred in the acetone-modified fluid. If the cosolvent is capable of self-association in supercritical carbon dioxide (methanol), then hydrogen-bonded cosolvent clusters are grouped around the solvate complexes even at low concentration of it. The number of molecules in such clusters can reach 10, although methanol associates consist of no more than three molecules in the fluid bulk.