We have studied the mechanism of the mechanochemical interaction between Na 2CO 3 and Nb 2O 5 in the initial stage of milling, before the final crystalline oxide product, i.e., NaNbO 3, is formed. In order to do this, the milling parameters were chosen to give a relatively low ball-impact energy. In addition, one of the reactants, i.e., Na 2CO 3, was milled also individually so that the mechanochemical effect on the separately milled compound could be determined. X-ray diffraction analysis, thermal analysis and infrared spectroscopy were used in order to characterize the samples after different milling times. The mechanochemical treatment of the Na 2CO 3–Nb 2O 5 mixture results in the formation of a carbonato complex, which represents an intermediate stage in the mechanochemical synthesis of NaNbO 3.