Single crystals of pure and mixed ZnSO4.7H2O and MgSO4.7H2O crystals were grown by slow evaporation method. The grown crystals were characterized by x-ray diffraction, atomic absorption spectral analysis and thermal analysis. The lattice parameters were calculated by from the XRD data. Atomic absorption spectral analysis showed that the Mg and Zn atoms were present in the mixed crystals. The thermal analysis by TGA and DTA showed that the mixed crystals have higher thermal stability than the pure crystals.