Extensive measurements of magnetic bubble mobility in epitaxial Sm0.4Y2.6Ga1.2Fe3.8O12films have shown that is is possible to obtain a uniformity of better than ± 15% over a 1.1 × 1.1‐cm area and an average mobility of 270 cm/sec Oe. This uniformity was obtained in films which were grown under carefully controlled conditions, whereas a variation in the mobility from 170 to 510 cm/sec Oe was observed in other films where the growth parameters were not as carefully controlled. The possibility that the growth rate and growth temperature might influence the mobility was investigated, but no correlation was observed. However, annealing at 1200°C was found to have a beneficial effect on the mobility when the mobility was abnormally low in the as‐grown state. The mobility was also observed to increase by a factor of ∼ 2 over the temperature range 25–80°C, and proton implantation at a dosage sufficient to suppress hard bubbles did not materially affect the mobility. The value of the damping parameter obtained from measurements of wall mobility was found to be in good agreement with the value obtained from measurements of the microwave resonance linewidth.