BACKGROUND Confirmation of food labeling that claims production in a small geographic region is critical to traceability, quality control and brand protection. In the current study, isotope ratio mass spectrometry (IRMS) was used to generate profiles of δ13C and δ15N to determine if the stable isotope signatures of Keemun black tea differ within the three counties that claim production. Other factors (cultivar type, leaf maturity and manufacturing process) were considered for their potential effects. RESULTS Both cultivar type and leaf maturity have remarkable impact on the δ15N values of tea leaves, and that the cultivar influenced the δ13C values. Keemun black tea from Qimen county could be easily discriminated from samples from Dongzhi and Guichi counties based on δ15N signatures. The k‐NN model was cross‐validated with an accuracy of 91.6%. Environmental factors and/or genotype seem to be the major reasons for δ15N differences in Keemun black tea from the selected regions. CONCLUSION This article provides a potential effective method to delineate the geographic point‐of‐origin of Keemun black tea based on δ15N signatures. © 2018 Society of Chemical Industry