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The Northeast China Transect (NECT) is a mid-latitude terrestrial transect in the International Geosphere-Biosphere Programme. Its major environmental gradient is precipitation, which gradually decreases from the eastern mountainous region to the western pastoral area. In this investigation, a series of forest and grassland soils were sampled along the NECT, and the denitrification rate and nitrogen/nitrous oxide (N2/N2O) ratio were studied under laboratory conditions by the acetylene inhibition method. Forest soils were all acidic, with soil pH values ranging from 4.3 to 5.9 and soil organic carbon ranging from 32.0 to 54.7?g?kg?1. Soil pH for grassland soils was approximately neutral, ranging from 6.1 to 7.8, while soil organic carbon ranged from 14.8 to 32.2?g?kg?1. The highest denitrification rates (average 1.1?±?0.2?mg?N?kg?1?h?1) were in grassland soils in the western part of the NECT, while the lowest were in forest soils (average 0.25?±?0.1?mg?N?kg?h?1) in the eastern part of the NECT. The denitrification rate increased linearly from east to west along the NECT (p?<?0.01). Nitrous oxide was the main component of gas products of denitrification in forest soils, while N2 was the dominant denitrification product in grassland soils. The ratio of N2/N2O increased linearly from east to west along the NECT (p?<?0.01). Soil pH was the best predictor of the denitrification rate and of the N2/N2O ratio in grassland and forest soils along the NECT.