Provided are, by using an index with which the influence on the strength of coke can be evaluated, a method for evaluating a weathering degree of coal and a coking property of weathered coal within the ranges in which the weathering degree and coking property cannot be determined by using conventional methods, and a method for controlling the weathering degree of coal with which it is possible to add weathered coal to a coal blend to be used for producing coke without decreasing the strength of coke by using the index. The weathering degree of coal is evaluated by using the surface tension of semicoke which is prepared by performing a heat treatment on weathered coal as an index. Moreover, the surface tension of each brand of semicoke which is prepared by performing a heat treatment on each of the plural brands of coal included in coal stock is previously determined. In addition, the proportion of each brand of coal to the whole coal stock is also previously assessed. The weathering degree of each brand of coal is controlled so that the interfacial tension ³ inter of a semicoke blend which is prepared by blending the plural brands of semicoke in accordance with the proportions is 0.03 mN/m or lower.