Abstract: A method for evaluating internal quality of fused cast refractories including the steps of: emitting electromagnetic wave pulses from sending and receiving antennas moving vertically in the vicinity of a side face of a refractory sample through the side face to an inner portion of the sample electromagnetic waves reflected by the sample via by the sending and receiving antennas, thereby obtaining crude reflected wave images; and evaluating an internal structure of the sample based on the picture of reflected wave images. By the present method, an entire inner structure of a fused cast refractory may be evaluated by emitting electromagnetic wave pulses through only by one side face toward a symmetry plane of said fused cast refractory about which the fused cast refractory is symmetrical, and receiving electromagentic waves reflected from an inner surface of the fused cast refractory sample.