Disclosed is a method for making an aluminum nitride substrate. At first, aluminum nitride is mixed with a carbonized material. The mixture is made into mixture powder in a granulation process. The mixture powder is sintered at an appropriate temperature so that the carbonized material reacts with oxygen to produce a gaseous carbon compound. The gaseous carbon compound is released, and hence an aluminum nitride substrate is made. Before the making of the aluminum nitride substrate is made, the aluminum nitride powder is mixed with the carbonized material. For the stable heat dispersion of the carbonized material, the heating is even during the sintering. The purity of the aluminum nitride substrate is high, the quality of the aluminum nitride substrate is good, and the size of the aluminum nitride substrate is large. Hence, the yield of the making of the aluminum nitride substrate is high.