In northern regions, spike-like N₂O emissions from soils are observed in early spring. During this period, snow melting can cause soil thawing, depending on the presence of a frost layer, i.e., the air temperature and the thickness of snow cover in early winter. Soil freezing is a known factor inducing soil denitrification. Our in-situ snow cover manipulation experiment in Hokkaido, Japan, revealed a large N₂O flux and increased N₂O concentration with decreasing O₂ concentration in the surface soil layer immediately after and before the snow-melting period, respectively. This was observed in a treatment plot with deep soil frost formation by snow cover removal until mid-winter. However, in our two-year (2008–2010) observation at this plot, greater maximum soil frost depth did not always result in larger N₂O flux. Therefore, we speculate that snow cover and snowmelt water in early spring play important roles in stimulating N₂O production as a heat insulator and gas diffusion barrier, respectively, thus creating warm and anoxic microsites in the frozen surface soil layer.