Yield and quality of chestnut (Castanea mollissima Blume) are affected by nitrogen (N) availability; however, there are few reports on foliar and root absorption of different chemical forms of N in chestnut. To analyze the absorption characteristics of exogenous N fertilizer labeled by ¹⁵N in chestnut, nitrate and ammonium nitrogen uptake and allocation were determined in 1-yr-old seedlings that received soil and foliar ¹⁵NH₄NO₃ and NH₄¹⁵NO₃. We found that 29% of the nitrate and 25% of the ammonium absorbed by the leaves were translocated to the roots, while 62.01% of the nitrate and 63.27% of the ammonium absorbed by the roots were translocated to the shoots. The seedlings absorbed more nitrate nitrogen than ammonium nitrogen, and their foliar N uptake was faster than their root uptake. Most of the N absorbed by the seedlings was fixed in the shoots in both foliar and soil uptake. The proportion of N fixed was greater in seedlings subjected to foliar fertilization than in those treated with soil fertilizer. Foliar fertilizer application can meet the N nutritional needs of fast-growing shoots more effectively than soil fertilizer application; however, soil fertilization was a better long-term N source than foliar fertilization. Thus, ensuring an adequate supply of nitrate N fertilizer in the soil accompanied by a commensurate increase in foliar fertilizer application can effectively meet the nutrient requirements associated with the rapid growth of chestnut seedling shoots.