As a valid seawater oxygen proxies, trace iodine in marine carbonates is crucial for reconstructing the redox conditions of the paleoceanography. Although highly sensitive inductively coupled plasma-mass spectrometry (ICP-MS) is often used for the determination of iodine, the accurately determining trace iodine of marine carbonates remains challenging due to its high volatility loss during the sample digestion and the matrix effect of coexisting high-calcium (Ca) in ICP-MS analysis. In this study, an ammonium bifluoride (NH4HF2) sample digestion ICP-MS method was evaluated for analyzing sub-μg/g levels of I in marine carbonate rocks. Results show that more than 97% of the target iodine can be well retained in the digestion solution, while simultaneously achieving the removal of the coexisting calcium matrix (over 86% of the calcium remains in the residue). The limit of detection (LOD, 3 sigma) the established method is 0.024 μg g-1 (taken into 250-fold dilution) with the relative standard deviation (RSD, N=5) ranging from 3.1 % to 8.0 %. The proposed method was applied to determination of I in a series of carbonate rock reference materials (RMs) and the satisfactory results (recovery, 87-104%) indicate that it has great potential for the determination of trace level I in various marine carbonate rocks.