The characteristic of the annealing of a pure aluminum sheet by the CW-CO₂ laser is examined. It is necessary to select a suitable laser irradiation condition to generate a full annealed part through the rear surface of the sheet. The irradiation conditions were the output of laser, the defocus distance from the focal point and the traverse speed of sample. The temperature necessary to acquire full annealing by the laser irradiation method is 1.4 times higher than that of the electric furnace method. The full annealing width estimated from the hardness distribution on the bottom surface spreads with higher output and larger defocus length, or smaller traverse speed. The minimum value of full annealed width is restricted by the appearance of molten part in the laser irradiated area. The maximum and minimum widths of full annealed region obtained under this experimental condition are 12.5 and 2.5 times larger than the thickness of sheet, respectively. By choosing suitable laser conditions, the annealing can proceed easily in the limited zone. However, it is difficult to keep the full annealed width to be constant. The full annealed width of the prescribed length might not be obtained until the temperature distribution reaches the steady state. On the other hand, the full annealed width extends at the final stage where the laser approaches the edge of the sheet due to the heat insulation effect of the edge. Therefore, the uniform width should be realized by controlling the condition such as the laser output, the defocus length and the traverse speed during laser irradiation.