Significant actinide redistribution was observed in the outer low-temperature region of uranium-plutonium mixed-oxide fuel Data from the large number of fuel pins examined indicated boundaries within which redistribution in the outer low-temperature regions of the fuel occurred. Plutonium redistribution was not observed in fuel pins with an initial fuel oxygen-to-metal ratio (O/M) of >1.98 or in fuel irradiated to burnups of <5.0 at.%. Fuel pins with an initial O/M ratio of 1.96 exhibited plutonium enrichments on the fuel outer periphery at a burnup of ≥5.0 at.%. At ∼6.5 at.% burnup, a transition in character of the actinide distribution occurred, resulting in plutonium enrichments in the equiaxed grain region and uranium enrichments on the outer periphery of the fuel. Increasing the fuel initial O/M to 1.97 decreased the burnup at which plutonium enrichment occurred near the equiaxed grain region from 6.5 to 5.0 at.%. Conversely, decreasing the initial O/M ratio from 1.96 to 1.95 increased the burnup at which plutonium enrichment occurred in the equiaxed grain region from ∼6.5 to ∼7.5 at.%.