This paper reports the transport kinetics of Mg in cubic yttria-stabilized zirconia (containing 10% mol of Y2O3 (10YSZ)) involving the bulk and the grain boundary diffusion coefficients. The diffusion-controlled concentration profiles of Mg were determined using secondary ion mass spectrometry (SIMS) in the range 1073-1273 K. The determined bulk diffusion coefficient and the grain boundary diffusion product may be expressed as the following functions of temperature, respectively: D = 5.7 exp[(-390 kJ/mol)/RT] cm(2).s(-1) and D'alphadelta = 3.2 X 10(-15) exp[(-121 kJ/mol)/RT] cm(2).s(-1), where a is the segregation enrichment factor and 6 is the boundary layer thickness. The grain boundary enhancement factor decreases with temperature from 10(5) at 1073 K to 103 at 1273 K.