Abnormal grain growth (AGG) is frequently observed in sintered (K, Na)NbO 3 (KNN)-based piezoceramics. However, in the present study, abnormal grain growth was unexpectedly discovered in calcined KNN-based powders. To explain the phenomenon, three well-established models that account for the AGG in sintered ceramics were discussed, including (a) liquid-phase-assisted grain growth, (b) two-dimensional nucleation grain growth, and (c) complexion coexistence.However, the AGG in calcined powders was concluded to be none of them, but a consequence of the A-site compositional inhomogeneity in the K 2 CO 3 -Na 2 CO 3 -Nb 2 O 5 ternary system. Since repeated calcination and ball milling have low efficiency on solving AGG and the accompanied compositional inhomogeneity, abnormal grains were found to coexist with normal grains at a very high calcination temperature, that is, 1000°C. The compositional inhomogeneity is believed to be remaining even after sintering and consequently deteriorate the comprehensive performances, which might be a determinant for the unstable reproduction of KNN-based piezoceramics.