Fragments of M(CH3SO3)(2)-H2O (M = Zn,Cu) phase diagrams from subsolidus temperatures up to 70 degrees C (343.15 K) were obtained. Melting parameters of anhydrous zinc methanesulfonate (T-m = 566.2 +/- 0.3 K, Delta H-m = 33.4 +/- 0.6 kJ/mol) were clarified. New dodecahydrate zinc methanesulfonate and octahydrate copper methanesulfonate were revealed and characterized. Space group (R-3), lattice parameters (a = 9.1711(2), c = 21.4910(5)) and structure of Zn(CH3SO3)(2)center dot 12H(2)O were determined. The dodecahydrate melts congruently at T-m = 299.4 +/- 0.1 K, with the enthalpy of fusion Delta H-m = 78.9 +/- 0.1 kJ/mol. The octahydrate Cu (CH3SO3)(2)center dot 8H(2)O melts incongruently at 254.9 +/- 0.1 K.