In this study, stable isotope signatures (C-13, N-15, and D) of both tea leaves and tea infusions were investigated to identify the geographical origin of Turkish domestic and imported tea samples. Sixteen domestic tea samples collected from different locations in the Black Sea Region, which produces almost 100% of tea in Turkey, and 11 imported tea samples (Kenya, India, Sri Lanka, Indonesia, and China) purchased from importers were studied. C-13, N-15, and D in the samples were determined using isotope ratio mass spectrometry (IR-MS). C-13 in the samples ranged from -29.18 +/- 0.01 to -25.7 +/- 0.2, while N-15 ranged between 1.1 +/- 0.2 and 5.2 +/- 0.8. However, D in the samples were found to be in the range from 56.5 +/- 0.3 to 72 +/- 1. The classifications of the tea samples into domestic and imported tea samples were achieved with 100% accuracy using multivariate statistical analyses (principal component analysis, PCA, and hierarchical cluster analysis, HCA). In conclusion, the domestic tea samples had a distinctive isotopic fingerprint and the isotopic ratios used in the study can be significant predictors in determination of the geographical source of Turkish tea.