In this study, it was attempted to enhance the performance of flotation cleaning of oil shales by use of ultrasound. The use of an excitation effect through ultrasonication was investigated towards inorganic particles that remain clogged in pores/voids or attached as surface coatings. Ultrasonic treatment was applied prior to flotation at different ultrasonic power levels and for different ultrasonication periods. Ultrasonic treatment proved to be useful in improving the extent of ash rejection. After ultrasonic treatment, the ash content of Himmetoglu oil shale decreased from 34.76% to 11.82% with 82.66% combustible recovery and the ash of Beypazari oil shale decreased from 69.88% to 34.76% with 64.78% combustible recovery. Comparative XRD and SEM analyses showed that particulates clogged in the pores/voids or attached to the surfaces of larger particles were effectively removed after ultrasonic treatment and this condition significantly improved the liberation between organic and inorganic entities. (c) 2008 Elsevier B.V. All rights reserved.