The apparent molal volumes (V-phi) of the trivalent rare earth (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) chlorides, nitrates and perchlorates have been calculated from the density measurements at 25 degrees C and (5 to 80) degrees C and 0.02 - 4 m. The values of V-phi have been fitted to the Pitzer equations, V-phi, = (V) over bar (0) + (A(v)I/(1.2m) In(1 + 1.2I(0.5)) + 2RTm(beta(v(0)) + beta(v(1)) g(y) + mC(v)), where (V) over bar (0) is the infinite dilution partial molal volume, A is the Debye-Huckel slope, I is the ionic strength, and g(y) = (2/y(2)).[1 - (1 + y) exp(-y)] where y = 2(I-0.5). The Pitzer volume parameters beta(v(0))), beta(v(1)) and C-v are functions of temperature. The values of (V) over bar (0), beta(v(0)), beta(v(1)), and C-v for most of the rare earth chlorides are similar orders of magnitude. These results should be useful in estimating the effect of pressure on the equilibria of rare earths in natural waters over a wide range of temperature.