Alpha-activities due to 239Pu and 240Pu of the three kinds of highly radioactive fallout particles, which originated from a Soviet large scale air burst carried out in autumn 1962, the first Chinese explosion (a small scale land surface burst) and the second Chinese explosion (a small scale air burst), respectively, have been measured alpha-ray spectrometrically, while their activities of 144Ce and 95Zr + 95Nb have been measured gamma-ray spectrometrically. The differences in specific activities and composition ratios of these nuclides which have been found among the three kinds of particles are discussed in connection with the differences in burst conditions among the three explosions from which they originated. The ratio of alpha-activity to total activity (alpha/alpha + beta) has been found to be considerably smaller in the particles than in the rain-water samples which were collected in the periods just before and after the days when the particles were found and collected. The Pu concentrations in the mean rain-water samples collected in the period from 1962 to 1965 were measured to be about 3 × 10−2 pCi/l.