Abstract: The largest bivalve shell in the world, the marine bivalve, Tridacna spp., has hard and dense aragonite shells with annual or daily growth lines in its inner shell layers, and is becoming an ideal material for high-resolution paleoclimate reconstructions. However, identification of shell calcilization is necessary before using Tridacnidae as paleoclimate recorders.Five Tridacnidae specimens were collected from the South China Sea. The analysis results of X-ray diffraction (XRD), differential scanning calorimetry - thermo gravimetric analysis (DSC-TGA) and gas chromatography-mass spectrometer (GC-MS) showed that all the Tridacna spp.’s inner shells studied here are entirely made of aragonite, and shell calcilization does not occur. The main inorganic compound of the inner shells is CaCO3, with a content between 96.5%~97.2%; the content of the organic matter, such as hexadecane and 17 kinds of amino acids, is between 2.8%~3.5%. However, calcilization takes place in some outer shell layers. This study presents a method to identify the calcilization of Tridacnidae shell, and preliminarily determines composition and content in Tridacnidae shell. Results from this study provide a basis for such reconstruction using Tridacnidae shells.