In this paper we present an optical derotator for scanning vibrometer measurements on rotating objects. The main part of an optical derotator is a rotating prism. Several concepts are known from literature. We have chosen a Dove prism because it can derotate the rotation of the specimen by simply watching through the prism, which rotates with half the speed. The design of our derotator is presented in this paper as well as a discussion of the system performance. In addition we show experimental measurement results on a fan rotating with 3000 rpm.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.