The Cs2Nb4O11 (CN) and Rb2Nb4O11 (RN) single crystals are grown by means of flux method and their physical properties are studied. Despite the similarity of their chemical formulae the crystals are not isostructural. CN crystals undergo ferroelectric phase transition at 164degreesC. Both the compounds show electrical conductivity of about 10(-4)O(-1) cm(-1) at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.