Single crystals of YB66 have been grown by the indirect heating floating zone method. The effects of growth rate and feed rod composition on the crystal quality were examined. The optimum growth rate was 25 mm/h. The congruent composition was confirmed to be [B]/[Y] = 62. Preliminary X-ray rocking curve analysis showed that the full width half maximum of the rocking curve of the best crystal was less than 12 min. © 1990, Elsevier Science Publishers B.V.. All rights reserved.