Large single crystal of Na2Ni (SO4)2.4H2O (NNSH) was grown for the first time using method of isothermal decrease of supersaturation. The crystal structure of NNSH is determined by single crystal X-ray diffraction method, which is far different from the structure of known nickel sulfate hexahydrate series compounds. The growth habit, optical transmission spectrum and thermal stability are first reported in this paper. Similar optical transmission spectrum with nickel sulfate hexahydrate (NSH) crystal shows that NNSH crystal can also been used as ultraviolet light filter (ULF). The dehydration temperature (tdh) is 132º, which is much higher than commercial available ultraviolet filters, this is correlate with the unique crystal structure of NNSH crystal.