| Summary: | This work presents the first use of Sr isotope ratios for determining the provenance of bovine milk from different regions of Slovenia. The analytical protocol for the determination of <sup>87</sup>Sr/<sup>86</sup>Sr isotope ratio was optimised and applied to authentic milk samples. Considerable variability of <sup>87</sup>Sr/<sup>86</sup>Sr ratios found in Slovenian milk reflects the substantial heterogeneity of the geological background of its origin. The results, although promising, cannot discount possible inter-annual or annual variation of the Sr isotopic composition of milk. The <sup>87</sup>Sr/<sup>86</sup>Sr ratios of groundwater and surface waters are in good correlation with milk, indicating that the Sr isotopic fingerprint in milk is reflective of cow drinking water. The <sup>87</sup>Sr/<sup>86</sup>Sr ratio has the potential to distinguish between different milk production areas as long as these areas are characterised by geo-lithology. Discriminant analysis (DA) incorporating the elemental composition and stable isotopes of light elements showed that <sup>87</sup>Sr/<sup>86</sup>Sr ratio together with <i>δ</i><sup>13</sup>C<sub>cas</sub> and <i>δ</i><sup>15</sup>N<sub>cas</sub> values have the main discrimination power to distinguish the Quaternary group (group 6) from the others. Group 1 (Cretaceous: Carbonate Rocks and Flysch) is associated with Br content, 1/Sr and <i>δ</i><sup>18</sup>O<sub>w</sub> values. The overall prediction ability was found to be 63.5%. Pairwise comparisons using OPLS-DA confirmed that diet and geologic parameters are important for the separation.
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