Magnesium carbonate precipitation by the reaction of MgCl2 with Na2CO3, using sodium tartrate as an additive was studied. The effects of sodium tartrate concentration, reaction temperature, and stirring speed on the precipitation were investigated comprehensively. Scanning electron microscopy (SEM) and X-ray powder diffraction methods were used to characterize the carbonate precipitate products. Sodium tartrate concentration, reaction temperature, and stirring speed have significant effects on the morphology of the carbonate products. Sodium tartrate has an inhibitive effect on the precipitation. The product weight decreases with the increase in the amount of sodium tartrate added, and with the increase in reaction temperature, but is almost irrelevant to the stirring speed. The products obtained at 25 and 50°C were all identified as nesquehonite. The experimental results show that the use of an additive would be an effective method to adjust the morphology of magnesium carbonate.