Two field experiments were conducted on Andisols in Japan to evaluate changes in natural ¹⁵N abun-dance in the soil profile and to estimate whether the values of δ¹⁵N can be used as an indicator of fertilizer sources or fertilizer fate.The 6-year experiment at the National Agricultural Research Center (NARC) consisted of the following treatments: swine compost (COMPOST), slow-release nitrogen fertilizer (SRNF), readily available nitrogen fertilizer (RANF), and no fertilization (CONTROL).Experimental plots at the Nippon Agricultural Research Institute (NARI) received cattle compost at different rates for 12 years;a forest soil at this site was sampled for comparison.Swine compost greatly changed δ¹⁵N distribution pattern in the soil profile, with the highest δ¹⁵N values occurring in the top 20-cm layer of the COM-POST plot, decreasing in the sequence of CONTROL\RANF> SRNF, mainly due to relatively high δ¹⁵N value of swine compost and its subsequent decomposition.In contrast, SRNF resulted in the lowest δ¹⁵N values in soil, indicating small nitrogen losses relative to input and low nitrogen release rates.Values of δ¹⁵N increased with compost applicat ion rates at NARI, and, for the unfertilized soil, the values of the FOREST plot at NARI were 1~2 δ units larger than the CONTROL plot at NARC.In leachate collected at 100 cm depth, δ¹⁵N values decreased in the sequence of COMPOST> RANF\CONTROL> SRNF.The lowest δ¹⁵N values of leachate of RANF plot was observed in the depth of 200~250 cm.These results in-dicated that δ¹⁵N values in upper soil or leachate may help us infer pollution sources of organic or inorganic nitrogen qualitatively in Andisols.