Effect of intensive grinding on the dissolution of celestite in acidic barium chloride and sodium chloride solutions was studied by investigating structural changes occurred during milling. Complete dissolution of the celestite was achieved within 25 min by milling in a planetary ball mill in which ball to ore ratio is 10. But, increasing grinding time and ball to ore ratio diminished the dissolution rate. X-ray amorphous phase content and XRD breadths increased and XRD line reflection intensity decreased with increasing of grinding time, and celestite does not undergo a considerable phase transformation during milling. SEM micrographs showed that how prolonged milling results in an increasing degree of agglomeration and a reduced amount of fines. Additionally, the ground samples were heated at elevated temperatures and then re-ground under earlier grinding conditions. Structural, morphological and dissolution characteristics of the samples obtained by each of the three treatments were also evaluated. It was concluded that high energy milling for short times increases the dissolution rate of celestite. But, increase in the particle size due to agglomeration or compactness of the particles as a result of impact stress predominant in planetary ball milling decreased the leaching rate, as grinding time and ball to ore ratio in the mill were increased. (C) 2008 Elsevier Ltd. All rights reserved.