Analysis of trace amounts of crystalline impurities such as sodium chloride (NaCl) and diacetylmorphine hydrochloride (heroin) in seized methamphetamine hydrochloride (MA·HCl) powders was carried out using synchrotron radiation X-ray diffraction (SR-XRD) at beam line BL19B2 in SPring-8 for the scientific drug investigation. The analytical results were compared with those obtained by the analysis method of using conventional XRD instrument. About one milligram of the MA·HCl powder was packed in a glass capillary tube with 0.3 mm inner diameter, and exposed to the monochromatic SR X-ray beam. The diffraction lines from the seized MA·HCl powder were detected and recorded using a imaging plate in a Debye Sherrer camera.   The peak width at half height for the SR-XRD at BL19B2 was found to be about half of that for the conventional XRD. Therefore small diffraction lines from trace impurities could be clearly separated from the other lines from major components. Some sharp lines originating from trace amounts of heroin and NaCl in a milligram quantity of the seized MA·HCl samples could be confirmed using the SR-XRD, whereas these lines could not be identified clearly by the conventional XRD. The advantages of the SR-XRD are simultaneous detection of trace crystalline impurities, including both organic and inorganic materials, in small amounts of MA·HCl samples, and rapid analysis with high angle resolution. This method should be very effective for the discrimination of illicit MA·HCl samples containing trace impurities.