The thermal expansion and heat capacity of coarse-crystalline (bulk) and nanocrystalline silver sulfide Ag2S have been studied by dilatometry and differential scanning calorimetry methods in the temperature interval from 290 to 970 K. The thermal expansion coefficient and heat capacity of nanocrystalline silver sulfide in the examined temperature range are larger than the same properties of coarse-crystalline sulfide. It is shown that these differences are due to a small particle size which leads to the restriction of the phonon spectrum on the side of low and high frequencies. It is established that the acanthite α-Ag2S to argentite β-Ag2S and argentite β-Ag2S to γAg2S phase transformations are the first-order phase transitions, and the temperatures and enthalpies of these transformations have been determined.