Natural nitrogen isotope abundance (δ¹⁵N) has been suggested as a potential indicator for discriminating organic vegetables from their conventional counterparts. However, little is known about the δ¹⁵N characteristic of cauliflower (Brassica oleracea L. var. botrytis) under organic production and how the application of chemical fertilizers could affect this characteristic. In this study, δ¹⁵N characteristics of cauliflower (including the intra-plant δ¹⁵N characteristic) and soil under different fertilization treatments were investigated under field conditions. Five treatments were laid out: control, chemical fertilizers (F4M0), organic fertilizer (F0M4), and chemical fertilizer in combination with organic fertilizer at the ratio of 3:1 (F3M1) and 1:3 (F1M3). Results showed that plant δ¹⁵N was positively correlated with fertilizer δ¹⁵N and plant root/flower was more sensitive to changes of fertilizer δ¹⁵N and soil δ¹⁵N than leaf/stem. Distribution of δ¹⁵N in different plant parts (especially in flower and leaf) was significantly changed when organic fertilizers were partially or totally substituted by chemical fertilizers, suggesting a comparison of flower δ¹⁵N and leaf δ¹⁵N might be applicable for the organic identification of marketed cauliflowers. Our results provide fundamental data for the soil- and fertilizer-specific crop δ¹⁵N database and indicate that the intra-plant δ¹⁵N characteristic could be helpful for organic cauliflower identification.