【Objective】Summer fallow after winter wheat is harvested in dryland on the Loess Plateau is a very common practice to save rain water, and restore soil fertility for the next crop. Nowadays, the content of nitrogen (N) (mainly in nitrate form) in the soil of the dryland as residue of the fertilizer applied to winter wheat is increasing steadily. As summer is the rainy season in this region, whether or not the high rainfall would increase NO₃^--N leaching loss is an important issue deserving further study. The method of adding ¹⁵N labeled nitrate after winter wheat is harvested in dryland is one to quantitatively explore fate of the residual fertilizer N in the dryland under summer fallow in the Loess Plateau, and hence to provide a scientific basis for managing N in dryland. 【Method】The ¹⁵N labeled fertilization micro-plot (Polyvinylchloride column, 25 cm diameter and 25 cm long) method was used to study fate of the residual fertilizer N in the dryland under summer fallow in a field experiment, which had five tracts of cropland and two N treatments set up with and without N application (0 and 30 kg N hm^-2). ¹⁵N labeled nitrate was mixed with the surface soil (0~15 cm) in the micro-plot at a rate equal to the content of the residual fertilizer N in the field after winter wheat was harvested. At the end of the summer fallow, soil samples throughout the soil profile (0~200 cm) were taken from the micro-plots, for analysis the contents of soil total nitrogen, NO₃^--N, and their ¹⁵N abundance. 【Result】 Results show that at the beginning of the summer fallow, the content of NO₃^--N accumulated in the 0~200 cm soil was quite high, ranging between 205 and 268 kg hm^-2 and averaging 244 kg hm^-2; At the end of the summer fallow, apparent NO₃^--N accumulation peaks were found in the soil, 40~80 cm in depth, and ¹⁵N abundance ranged between 0.408% and 0.482% and averaged 0.429%, being the highest in the soil 60 cm in depth, averaged 0.372% in the soil 80 cm in depth, being higher than the background value of ¹⁵N abundance in the soil (0.367 ¹⁵N atom%), and was 0.369 % in the soil 100 cm in depth, more or less the same as the background value, in Treatments N30 in all the five tracts of cropland. In the five tracts of cropland, ¹⁵N labeled nitrate abundance was the highest in the 40~60 cm soil layer in the soil profiles (0~100 cm), averaging 2.151%; and the lowest abundance was in the 80~100 cm soil layer, averaging 0.407%, both significantly higher than the background value. Although the rainfall during the summer fallow season was only 157 mm, making it a dry year, it still leached ¹⁵N labeled nitrate down to 80 cm in depth, through a 45~65 cm thick soil layer, and even ¹⁵N labeled nitrate was found in 100 cm depth. At the end of the fallow, the content of residual N averaged 21.6 kg hm^-2 or ranged between 20.8 and 22.9 kg hm^-2 in the 0~100 cm soil profile, accounting for 71.9% of the applied N fertilizer in all the five tracts of cropland. The content of residual labeled N was 4.5 kg hm^-2, 2.9% of which was in the form of NO₃^--N in the 0~20 cm soil layer; Residual fertilizer N was mainly distributed in the 40~60 cm soil layer, and averaged 17.7 kg hm^-2 in content, accounting for 52.8% of the total N fertilizer applied, in which ¹⁵N labeled nitrate content was 6.8 kg hm^-2. After the summer fallow, the applied ¹⁵N labeled N fertilizer was found lost at a rate of 23.8%~30.8% (averaging 28.1%).【Conclusion】 Residual fertilizer N accumulated significantly in the 0~200 cm soil layer of the dryland after wheat was harvested, posing a potential risk of leaching. In 2014, though it was a dry year, the effect of rain water leaching NO₃^--N was still quite significant, indicating that the NO₃^--N leaching in the dryland during the summer fallow season should not be ignored and further studies should be done on mechanisms of its leaching loss.