In the poisonous incident case occurred in Japan. clarification of the identity between seized poisons and retrieved from crime scene is strictly required from the court. In this case, arsenous acid was used as a poisonous material and., seized one from suspect's house was only twenty particles. The synchrotron X-ray fluorescence spectrometry by comparing the intensity ratios of Lalpha line of four heavy metal, such as Bi, Sn, Sb, Se to Kbeta line of As was performed to overcome this problem. In this paper, the evaluation of this new method using 13 authentic arsenous acid samples, 4 of 13 were refined by Chinese method, 7 of 13 were refined by Japanese method (Sumitomo mining Co. Ltd. method), 2 of 13 were refined by German and Swiss method. As a result, by the comparison of the ratios of these four elements to As, these 13 samples were, clearly classified to three products classes produced by different refining methods. (C) 2004 Elsevier Ireland Ltd. All rights reserved.