Surface properties of styrene-tetrahydrofuran (St-THF) block copolymers (AB and ABA type) were studied. Morphology observed by electron micrography showed the formation of fibrils of poly-THF covered with poly-St for THF-rich block copolymers and the accumulation of poly-THF segments for St-rich block copolymers. The poly-THF segment was found to have a surface of activity 3 dyne/cm lower than the poly-St segment. Modification of the poly-St surface by adding St-THF block copolymers was examined by measuring the surface tension drop during heating. Inverse gas chromatography of the block copolymers revealed that the surface of St-rich block copolymer changes from poly-St to poly-THF on baking. The contact angle of water droplets was a linear function of surface composition, and water wettability of St-rich block copolymers by accumulation of surface active poly-THF segment was indicated.