A nanostructured AgI powder has been synthesized. The structure, sizes, and shapes of nanopar- ticles of the initial powder and a powder modified in a VIBRATOR GM-945B vibration ball mill have been investigated by SEM, X-ray diffraction, and differential thermal analysis. A hypothesis of the structure and microscopic mechanism of structural transformations in the materials under study is proposed. Particular attention is paid to the ac ionic conduction of silver iodide particles.