Sodium sulfate was obtained as a by-product in a process applied to fabricate boric acid crystals from borax solution with concentration of 155 g B2O3/1000 g solution, which contained around 65 g Na2O/1000 g solution and prepared from borax ore. Sodium sulfate crystallized before and after crystallization of boric acid had purities of betweea 95-98,5% and the purity was increased over 99% by refining. XRD analysis of sodium sulfate powders indicated that sodium sulfate were crystalline and contained only single phase. DTA-TG of sodium sulfate crystals were consistent with the data given in the literature. SEM investigation of sodium sulfate crystals revealed that, sodium sulfate particles had large angular particles of between 100-300 mum with octahedral morphology and revealing no agglomeration between the particles.