The solubility and the metastable zone width of sodium tetraborate decahydrate in solutions containing lithium chloride have been measured at temperature a range of (20 to 35) degrees C. It is found that the lithium impurity has a salt-in effect on the solubility of sodium tetraborate decahydrate. The metastable zone width broadens with an increase of the impurity concentrations. This increase can be attributed to the absorption mechanism on the crystal surface. The apparent nucleation order of sodium tetraborate decahydrate with and without impurity was calculated by a modified regression method. The results show that the addition of lithium impurity has no great effect on the apparent nucleation order of sodium tetraborate decahydrate.