Molecular dynamics simulation of molten Li2CO3and Na2CO3has been performed. The parameters of the pair potentials have been obtained from MO calculation by using a 3–21 G basis set. Comparison of structure of Li2CO3with Na2CO3reveals that the difference in predominant position of the cations with respect to the neighbouring anion may be explained in terms of the difference in the ionic radii of the cations. Some dynamic properties such as self-diffusion and rotational motion of the anion are also discussed in relation to the structures.