The densities of divalent transition-metal perchlorates in acetonitrile have been measured at (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, and 323.15) K. From these densities, apparent molar volumes, V-&UPhi; I and partial molar volumes of the salts at infinite dilution, V-&UPhi;(0), as well as the expansibilities, α(0)(V), have been evaluated. Moreover, the apparent molar isenotropic compressibility, K-S,(&UPhi;), of transition-metal perchlorates in acetonitrile have been determined from a sound velocity measurement at T = 298.15 K.