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Efforts have been paid to the estimation of defect size in ultrasonic inspection of weld parts, but very few attention has been focussed upon the identification of the kinds of defects in the inspection. A spectrum analysis technique was introduced to investigate this situation. Various kinds of weld defects such as crack, lack of penetration, lack of fusion, slag inclusion and porosity were artificially produced for the experiment using about 100 pieces of steel plates. The frequency distribution of the echoes reflected from these defects were analyzed with a spectrum analyzer. The experimental results indicate that when a proper gate interval is emproyed the spectrum of crack echo shows many indentations in the envelope, whereas that of other defect echoes show comparatively smooth envelopes. This result suggests the possibility of identifying cracks from other weld defects with the application of spectrum analysis.