Dolomite [CaMg(CO?)?] is a major carbonate mineral playing a critical role in various geological processes. Its carbon isotopic composition (δ13C) serves as an irreplaceable tracer for understanding Earth’s history and the deep-time global carbon cycle. Secondary ion mass spectrometry (SIMS) is one of the most dominant techniques for dolomite C- isotopic analysis. However, the widespread application is hindered by a shortage of high-quality dolomite standards. Furthermore, the classical off-line procedure, which is both inaccurate and inefficient due to its need for extra electron probe microanalyzer (EPMA) chemical compositions to calibrate the instrumental mass fractionation (IMF), poses a practical limitation. This study reports three new dolomite C-isotopic microanalysis standards (1001, 1026 and 1055) with Fe# values [molar Fe/(Mg + Fe)] varying from 0.02 to 0.35. By the concurrent SIMS measurement of 13C?12C?56Fe16O?24Mg16O, an accurate and rapid online matrix effect calibration method for dolomite C-isotope analysis was developed. The overall uncertainty for individual sample analyses was estimated to be ±0.9‰ (2SD), derived by propagating the measurement precision and the calibration residuals in quadrature. The new method concurrently determines δ13C and the 56Fe16O/24Mg16O ratio (a proxy for Fe#) in a single SIMS analysis, enabling accurate matrix-effect calibration that eliminates biases caused by spatial mismatch between separate EPMA and SIMS analytical domains. The advancement in accuracy and efficiency, as demonstrated by SIMS carbon isotope analysis of dolomite, has the potential to significantly enhance the fidelity of reconstructing ancient environments, establish more robust boundaries for carbon cycling, and refine the interpretation of geological records.