Barium carbonate (BaCO3) crystals with different morphologies were synthesized using BaCl2·2H2O by a carbonation method in water/ionic liquids (ILs) mixed solvents. The as-prepared products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the results indicated that the types of ILs and the mole ratio of water to ILs played important roles in determining the morphologies of the products. The analysis of the XRD pattern showed that ILs had an influence on the crystallinity of BaCO3. When the mole ratio of water to ILs increased, the size of BaCO3 crystals increased and the morphology gradually changed from spherical to oval and rod-like. A microemulsion model was employed to explain this mechanism.