A field experiment was conducted to examine the effect of frozen soil on Pratylenchus penetrans population density in Tokachi district, Hokkaido. After removing snow twice in February from the soil surface, the minimum temperature of the soil at 10cm reached-6.7•Ž and the frozen soil depth reached 20cm. Freezing did not occur in the soil covered with snow. At the end of March, P penetrans population densities in the snow-removed plots were 30-50% at soil depths of 0-10cm, 65% at depths of 10-20

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... cm less than those in the snow-covered plots. No significant difference in P penetrans population was found between two plots at depths of 20-30cm, where freezing did not occur. At planting in May, the total numbers of P penetrans decreased by 30-50% in the snow-removed plots. Frozen soil can affect the survival of P penetrans.