Strontium barium niobate (SBN, (Sr0.61Ba0.39)(0.5015)(Nb2O5)(0.4985)) was grown by using Stepanov technique (ST) or double crucible Stepanov technique (DCST). DCST is a modified Stepanov technique in which the inner crucible is introduced to reduce the temperature fluctuation inside the die. The change of refractive indices was estimated from the interference fringe of the grown crystal. In addition, the change in Sr concentration was estimated by using the relationship between the composition and the extraordinary refractive index. The local variation in the refractive index of the crystal grown by DCST is less than or equal to 3 x 10(-5) and is 1/3 of the value of the crystal grown by ST. The corresponding fluctuation in Sr concentration for the crystal grown by DCST is 0.0003, which is 1/3 of the value of the crystal grown by ST.