Activation energy for thermal desorption of dysprosium from a tungsten microcrystal of about 300 nm diameter was determined by means of the field-emission method. The desorption was detected from the whole W emitter surface in the temperature range 1490-1665 K for dysprosium average coverage theta < 0.06 monolayer. The average activation energy was determined to be 4.09 +/- 0.06 eV/atom and the frequency factor to be about 10(11) s(-1). The energy may mainly concern the desorption from the atomically rough regions of the microcrystal. (c) 2005 Elsevier B.V. All rights reserved.