Novel data on complexation of benzoic acid by parent and hydroxypropylated cyclodextrins were obtained by densimetry and H-1 NMR. Formation of 1: 1 inclusion complexes was detected in most cases with the exception of hydroxypropyl-gamma-cyclodextrin, which is able to form 1: 2 complexes. The data demonstrated penetration of carboxylic group of benzoic acid inside macrocyclic cavity, its insertion into beta-cyclodextrin cavity being deeper. Binding constants and volumes of transfer were calculated and analyzed in terms of influence of cyclodextrin structure on binding mode and driving forces of interaction as well as on the complex stability. (C) 2011 Elsevier B. V. All rights reserved.