Upon reduction, originally fully transparent and insulating ytterbium alumina garnet single crystals, Yb3Al5O12, become deeply colored and electrically conducting with a conductivity of the order of 10(-3) Omega(-1) cm(-1) in the temperature range of 550 degrees C to 1000 degrees C. The redox kinetics of the material is studied by means of conductivity relaxation experiments performed at oxidising and reducing conditions. Good agreement is obtained with an optical study into the redox kinetics of Yb3Al5O12. (c) 2006 Elsevier B.V. All rights reserved.