Boron compounds are very important raw materials in many branches of industry and their uses have been increasing and expanding continuously. Colemanite, one of the most common boron minerals, has a monoclinic crystal structure with a chemical formula of 2CaO·3B2O3·5H2O and is used usually in the production of boric acid. The present study concerns an investigation of the dissolution mechanism of colemanite in H2SO4 solution and the effect of acid concentration, the effect of SO4.2 ion on the dissolution process, using H2SO4, HCI+H2SO4 and H2SO4+Na2SO4 solutions. The analysis of the experimental data shows that increasing H3O+ acid concentration increased the dissolution rate, but increasing SO4.2 concentration reduced dissolution rate because of the precipitation of a solid film of CaSO4 and CaSO4·H2O.