We investigate the magnetization in the arrays of submicrometer-size disks fabricated from an epitaxial Fe layer grown on GaAs(001). The Fe disks having a layer thickness of 20 nm undergo a transition between multiple and single magnetic domains when their diameter is about 100 nm. Remarkable temperature dependence is found in the characteristics of the magnetization. (1) The saturation magnetization increases with decreasing temperature. While the low-temperature increase is more pronounced for smaller disk diameters, it is independent of the magnetic-domain state in the disks. (2) Magnetic hysteresis exhibits two-component-like behavior at low temperatures for ultrasmall disks. The additional component that emerges with lowering temperature gives rise to slow saturation of the magnetization, and is possibly responsible for the low-temperature increase of the saturation magnetization.