This paper contains a description of a new method of coke reactivity testing, which makes it possible to evaluate the degree and intensity of degradation of coke grains with various initial sizes. The results of coke reactivity testing with the use of this method are presented including degrees of mass decrement of coke samples with various initial grain sizes, decrement of average-size grain of tested coke during its gasification and mechanical resistance of coke samples after gasification. Based on the test results, the conditions were determined, under which determination with the use of the new method is carried out, as well as coke reactivity evaluation indices were specified. The new testing method has been verified, under Sendzimir Steelworks conditions, as for the possibility of using it to evaluate the impact of coke granularity on the course of the blast-furnace process.