Diffusion profiles of Sr in single‐crystal MgO at 1473 to 1843 K have been determined by a depth‐profiling technique using secondary ion mass spectrometry. The diffusion experiments were performed using a focusing infrared furnace. The temperature dependences of lattice and dislocation diffusion areD1= 2.6 × 10−11exp(–268.2/RT[kJ/mol])[m2.s‐1],Dd= 1.7 × 104exp(–562.3/RT), respectively. The present lattice diffusion coefficients are three orders of magnitude smaller than those previously reported. Si diffused with Sr in MgO over 1583 K, and the diffusion coefficients of Si were also determined. The results of Si diffusion were equivalent to those of our p