We measured the neutron diffraction of a single crystal of KOD-doped DO ice that annealed for 530 h at just below the phase transition temperature T-c = 76 K, to investigate the ice Ih to ice XI phase transition (i.e.. deuteron disorder to order). We obtained the evidence of the deuteron ordering with annealing: during annealing, the intensity of the 131 diffraction peak in ice XI increased with time and leveled off, which indicated the growth of domains with the deuteron-ordered arrangement. On the basis of the analyses of the change of the diffraction profiles, we estimate the time- and temperature-dependence of the deuteron ordering in ice. The results imply that the ice XI domains in KOD-doped ice increase with increasing time and with increasing temperature up to T-c.