Amounts of239Pu in alpha-bearing wastes were determined by -ray measurement using a NaI/Tl/ scintillation detector. The deviations of measurement caused by the nonuniform distribution of239Pu in the wastes and by a volume factor were corrected by rotating and scanning the objects. Contribution from241Am coexisting with239Pu was also corrected by taking into account the difference of the counts between A /356–470 keV/ and B /475–620 keV/ intervals. Attenuation of -ray of239Pu was estimated from the matrix density. Thus the content of239Pu could be determined within an accuracy of about 25% at the 1 mg level in a cardboard carton of 17 1.