Abstract: Structural carbonate is found within apatite from eclogites in the southeastern part of the Dabie Mountains. The apatite is mainly hosted in the diablastically textured garnet. Euhedral hexagonal or needle-like apatite occurs at an earlier stage of metamorphism than the garnet and the eclogitic assemblages. Apatite has a small diameter between 0.02 and 0.07mm，which is averaged 65 times smaller than the host garnet. X-ray diffraction and Faurier transform infrared spectroscopic studies show that all of the apatite has detectable amount of structural carbonate. It is identified to substitute [PO4]3-, but its amount cannot be measured by the traditional spectroscopic methods. An EA-MS online measurement gives a wide range of structural carbonate content(0.95～5.24 CO2wt％). The high C content is attributed to the contribution from the other kinds of carbon, such as the fluid inclusion or the carbonaceous film in the micro-crack. As a result, the spectroscopic calibrated values are always lower than the EA-MS online ones because significant amounts of structural carbonate show no signa1. Both identification of structural carbonate within apatite from eclogites and the quantitative measurement of bulk carbon concentration in the apatite demonstrate the presence of CO2-bearing fluid during ultrahigh pressure metamorphism in the Dabie Mountains.