[en] Unfissioned plutonium (^239+240Pu) along with fission products (including ¹³⁷Cs) were released from the Nagasaki A-bomb on 9 August 1945 and deposited in the eastern side (Nishiyama) of the city of Nagasaki. The concentrations of these radioactive materials were determined in 47 undisturbed surface soils collected from both eastside and westside of the hypocenter. The maximum concentrations were 64.5 mBq g^-1 (dry) (or 181 mBq cm^-2) for ^239+240Pu and 188 mBq g^-1 (dry) (or 526 mBq cm^-2) for ¹³⁷Cs in the Nishiyama district where 'black rain' precipitated 20 min after the detonation. The ratio ^239+240Pu/¹³⁷Cs was not constant in the soil samples collected from the Nishiyama. The maximum ratio (73.8%) was observed 2.8 km east of the hypocenter, where the maximum ^239+240Pu concentration was observed. This finding suggests that there was fractionation between ^239+240Pu and ¹³⁷Cs during 'black rain' formation. Previously reported data support this fractionation hypothesis for the Nishiyama local fallout. (author)