Reliable Sr isotope analysis of carbonate rocks requires effective separation of non-carbonate phases that can bias both radiogenic (R(87Sr/86Sr)) and stable (δ88Sr/86SrSRM987) isotope measurements. While sequential leaching has been evaluated using the R(87Sr/86Sr), the behavior of δ88Sr/86SrSRM987 during this process remains poorly constrained. Here, we systematically investigate the evolution of both radiogenic and stable Sr isotopes across sequential leaching steps in three carbonate reference materials, JLs-1, JDo-1, and NIST SRM 1d. This study reports new δ88Sr/86SrSRM987 data for individual leaching fractions of carbonate reference materials and provides the first sequential leaching–based Sr isotope dataset for NIST SRM 1d, for which both radiogenic and stable Sr isotope data have previously been limited. Early leaching fractions are dominated by surface-adsorbed and exchangeable Sr, whereas later fractions reflect contributions from clay minerals, both of which produce isotopic signatures distinct from primary carbonate phases. Only intermediate fractions yield reproducible Sr isotope compositions representative of primary carbonate minerals. The R(87Sr/86Sr) values obtained from bulk leaching differ from those of the intermediate fractions by more than analytical precision, whereas smaller but detectable effects (~0.03‰) are observed for δ88Sr/86SrSRM987, especially in clay-rich samples. Applying the carbonate-dominated leaching range, representative values of carbonate reference materials are obtained with R(87Sr/86Sr) of 0.707783±0.000028, 0.707386±0.000028, and 0.708008±0.000028, and δ88Sr/86SrSRM987 of 0.252±0.035‰, 0.256±0.035‰, and 0.325±0.035‰ for JLs-1, JDo-1 and SRM 1d, respectively (2SD). These results demonstrate that not only R(87Sr/86Sr) but also δ88Sr/86SrSRM987 are sensitive to phase-specific Sr released during leaching and highlight the necessity of accurate pretreatment for Sr isotope analysis. The dataset and analytical framework presented here expand the application of sequential leaching from Sr isotopes and improve the utility of carbonate reference materials for high-precision isotope studies.