Ga:YIG films which have partial replacements of Y by Gd or Eu, and which were grown on (111) and (100) Gd3Ga5O12substrates near 900°C by liquid phase epitaxy, show annealing effects in air and oxygen between 800 and 1200°C. The uniaxial anisotropy has a nearly linear variation with the film‐substrate lattice mismatch, indicating a stress‐induced anisotropy. The magnetic moment, coercivity, domain mobility, and optical absorption changes which occur as a result of annealing are also noted in this temperature range.