Hydrated calcium borates are the useful chemical industrial materials not only used in glass, pottery and porcelain enamel industry but also used in the fire protectants.However, the relatively large size of a metal borate as the flame retardant is hardly dispersed in a polymer matrix, which restrains its uses in industry.In addition, the morphology of material also greatly affects its properties.Therefore, in the past few years, much attention has been paid to the preparations and applications of borates nanomaterials.Up to now, there were a few reports on the preparation of calcium borates with nanostructures [1-4].In this paper, two kinds of morphologies for calcium borate 2CaO·B2O3·H2O nanobelts and fan-shaped 2CaO·B2O3·H2O nanostructure constructed by nanobelts have been synthesized under hydrothermal conditions at 180℃ with CaCl2, H3BO3 and NaOH as raw materials.All the samples were characterized by the XRD, IR, and SEM.The flame retardant properties of the prepared 2CaO·B2O3·H2O nanostructure were investigated by the thermal analysis method.The experiments show that the smaller size of nanostructure and the more uniform morphology, the better flame retardant property of the sample.