Spheroidal vaterite CaCO3 composed of irregular nanoparticals have been synthesized by a fast microwave-assisted method. The structures are fabricated by the reaction of Ca(CH3COO)(2) with (NH4)(2)CO3 at 90 degrees C in ethylene glycol-water mixed solvents without any surfactants. The diameters of the spheroidal vaterite CaCO3 range from 1 to 2 mu m, and the average size of the nanoparticals is about 70 nm. Bundle-shaped aragonite and rhombohedral calcite are also obtained by adjusting the experimental parameters. Our experiments show that the ratio of ethylene glycol to water, microwave power, reaction time, and two sources of ammonium ions and acetate anions are key parameters for the fabrication of spheroidal vaterite CaCO3. A possible growth mechanism for the spheroidal structures has been proposed, which suggests that the spheroidal vaterite CaCO3 is formed by an aggregation mechanism. (C) 2010 Elsevier B.V. All rights reserved.