Fabrication of advanced electronic components requires high-quality powders. In this work, nano-powders of Li or Na niobates are synthesized from (Li or Na)-Nb ethoxide by a sol-crystal method. A single crystal of (Li or Na)-Nb ethoxide is decomposed to an amorphous matrix below 473 K. Next, small crystals are grown by heating at the appropriate temperature for each specimen. The sol-crystal method provides homogeneous quality and fine grains by heating at lower temperature. Structural analysis of the powders is performed by a transmission electron microscope (TEM) and X-ray diffraction. As a result, LiNbO3 turns to dense-powders, but NaNbO3 forms nano-porous powders. In order to understand this difference, we try to observe in-situ the crystallization and grain growth processes by high-temperature TEM. We successfully observe in-situ this processing and discuss the structural change and formation mechanism of LiNbO3, comparing these features with those of NaNbO3.