Measurements of 239, 240Pu and 90Sr were performed on air-dust samples collected by means of filtration with cellulose-asbestos filter at Ibaraki prefecture, Japan during 1974 to 1979. The ranges of 239, 240Pu and 90Sr content determined in these samples are 0.041-1.9 microBq/m3-air (1.1-52 aCi/m3-) and 2.3 87 microBq/m3-air (0.062-2.3 fCi/m3) respectively. The activity ratios of 239, 240Pu/90Sr are found to be in a range between 0.008 to 0.026 with a mean value of 0.017. General trend on time variation of the content of 239, 240Pu and 90Sr in the surface air was in similar pattern each other. The content of these nuclides increased after the Chinese nuclear test explosions, and also in spring seasons with the exception of a few cases.