The effect of 5,11,17,23-tetrakis(diisopropoxyphosphonyl)-25,26,27,28-terapropoxycalix[4]arene on the chromatographic separation of ecologically hazardous aromatic compounds Aim. To study the effect of 5,11,17,23-tetrakis(diisopropoxyphosphonyl)-25,26,27,28-tetrapropoxycalix[4] arene additive to the MeCN/H 2 O mobile phase on selectivity of the HPLC separation of aromatic compounds using a Zorbax ODS support. Results and discussion. Calixarene improves the separation due to formation of the Host-Guest inclusion complexes. The linear dependence of 1/k' on the calixarene concentration allows calculating the stability constants К А of the complexes. The correlation of the separation selectivity induced by the calixarene additives with the ratio of the stability constants of the Host-Guest inclusion complexes of the aromatic analytes was found. The complexation is influenced by logP and pKa parameters of the analytes. Short contacts between the calixarene Host and the aromatic Guest indicate that the inclusion complexes are stabilized by various hydrogen bonds, nonvalence van der Waals, π-π and hydrophobic interactions. Experimental part. The energy minimized structures of the calixarene complexes with p-fluorophenol, guaiacol, toluene and trichloromethylbezene were calculated using Hyper Chem 8, PM3, vacuum. Conclusions. The data obtained can be used in design of new phases for HPLC.