The sulfate ion is one of the contaminations in natural salt. This impurity affects on quality and taste of culinary salt. One of the salt purification methods is SALEX process. In this method, saturated saline is used for extraction of impurities from salt. In this study effective parameters for removing of sulfate contamination are considered in SALEX method. At first the effects of salt particles size, washing time, saline volume to salt weight ratio and hardness of saline (according to calcium carbonate) were studied. Then the effects of all parameters, with random quantity, were considered synchronizely. Finally all data analyzed by statistical methods. The main and mutual effects are obtained by factorial analysis of variance. The results show that the maximum removal of sulfate are obtained by using of 0.25 mm particles size during 10 minute washing time with 10 to 1 (ml/g) ratio of saline/salt and 125 – 175 mg/l calcium carbonate concentration in washing solution.