The molal enthalpies of solution of VOSO(4)center dot nH(2)O (n = 4.21, 3.90, 3.00, and 2.63) at various molalities in water, Delta(sol)H(m), were measured by a solution-reaction isoperibol calorimeter at (298.15 +/- 0.01) K. The standard molal enthalpies of solution of VOSO(4)center dot nH(2)O(s), Delta(sol)H(m)(0)(n), were determined according to Archer's method. The standard molal enthalpies of solution for anhydrous VOSO(4)(s), Delta(sol)H(m)(0) = (-49.19 +/- 0.65) kJ center dot mol(-1), were obtained using extrapolation, and relative apparent molal enthalpies, phi(L), of aqueous VOSO(4) were calculated. In terms of the Bjerrum theory for ion association and the values of phi(L), the enthalpy of reaction for the formation of the ion pair [VOSO(4)](0), Delta(as)H(m)(0) = (3.42 +/- 0.04) kJ.mol(-1), was estimated using a semiempirical method.