The decrease in snowpack amplifies soil freeze-thaw cycles and decreases the snowmelt water supply to soil. This study examined how snow decrease affects the N mineralization and nitrification of forest soil in northern Japan by conducting an in situ experimental manipulation of snowpack and laboratory incubation studies of soil with differing moisture, temperature and freeze-thaw magnitude. For the incubation studies, surface mineral soil was collected and incubated using the resin-core method during the winter. In the field, there were two treatments: 50% and 100% snow removal, in addition to control plots. The 100% removal of snowpack significantly increased net N mineralization and marginally decreased the net nitrification in soil with the increase in freeze-thaw cycles. However, the net nitrification rates decreased in spite of the increase in ammonium-N availability. The results indicate that winter climate change, which alters the snowpack regime, would strongly impact N biogeochemistry through the increase in ammonium availability for plants and microbes, whereas it would be unlikely that the nitrate loss from surface soil would be enhanced.