The structure and chernical composition of the cork of Calotropis procera (Ait.) R.Br. were studied and comparison was made with composition and properties of cork from Quercus suber. The cells are approximately prismatic, thin-walled, and show appreciable cell wall wrinkling. Average dimensions are 100 µm in radiallength and 20 x 10-6 cm2 in tangential surface area, but considerable dimensional variability was found. Calotropis cork contains a large amount of inorganic material: 21.5 % of ash. Extractives' content is 11.1 %, of suberin 5.3 %, of lignin 40% and of polysaccharides 25.7%. Arabinans are the main hemicelluloses. The chemical composition of Calotropis cork significantly differs from Quercus suber cork, and this fact may partl y explain the different properties of these two materials.