The article describes the preparation of epoxy-calcium carbonate nanocomposites using diaminodiphenyl sulfone (DDS) as a curing agent. The curing behavior of diglycidyl ether of bisphenol-A (DGEBA) (1 mol) in the presence of varying amounts of nanocalcium carbonate was investigated by differential scanning calorimetry (DSC) using stoichiometric amounts of diaminodiphenyl sulphone (0.5 mol) as curing agent. The amount of calcium carbonate (similar to 44 nm) was varied from 2% to 10% (w/w). In the DSC scans of these samples, a broad exothermic transition due to curing was observed in the temperature range of 110-335 degrees C. As expected, heat of curing decreased with increasing amount of nanocalcium carbonate; however it did not affect the curing characteristics, thereby indicating that the filler did not hinder the curing reaction. Thermal stability of DGEBA in the presence of varying amounts of nano-CaCO3 after isothermal curing [(i.e., by heating in an air oven at 80 degrees C (1 h), 100 degrees C (1 h), 120 degrees C (1.5 h), and 180 degrees C (4 h)] was evaluated by thermogravimetry. All the samples were stable upto 350 degrees C, and char yield at 800 degrees C increased with increasing amount of nanocalcium carbonate. Rectangular bars were prepared by mixing DGEBA, DDS, and varying amounts of CaCO3 Using Silicone mold. The nanocomposites were characterized by Xray, scanning electron microscopy (morphological characterization), and dynamic mechanical analysis. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2161-2168, 2009