Bio-based calcium carbonate nanoparticles (CaCO3) were synthesized via size reduction of eggshell powder using mechanical attrition followed by high intensity ultrasonic irradiation. The transmission electron microscopic (TEM) and BET surface area measurements show that these particles are less than 10 nm in size and a surface area of approximate to 44 m(2)/g. Bio-based nanocomposites were fabricated by infusion of different weight fractions of as-prepared CaCO3 nanoparticles into Polylite (R) 31325-00 resin system using a non-contact Thinky (R) mixing method. As-prepared bio-nanocomposites were characterized for their thermal and mechanical properties. TEM studies showed that the particles were well dispersed over the entire volume of the matrix. Thermal analyses indicated that the bio-nanocomposites are thermally more stable than the corresponding neat systems. Nanocomposite with 2% by weight loading of bio-CaCO3 nanoparticles exhibited an 18 degrees C increase in the glass transition temperature over the neat Polylite 31325 system. Mechanical tests have been carried out for both bio-nanocomposites and neat resin systems. The compression test results of the 2% Bio-CaCO3/Polylite 31325 nanocomposite showed an improvement of 14% and 27% in compressive strength and modulus respectively compared with the neat system. Details of the fabrication procedure and thermal and mechanical characterizations are presented in this article. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1442-1452, 2013