alpha-form of imatinib mesylate and method of production thereof

The present invention provides a process for preparing crystals of mesylate alpha-form of imatinib substantially pure, which preferably comprises the crystallization imatinib mesylate from an organic solvent solution containing imatinib and the methanesulfonic acid dissolved therein, and seed crystals of mesylate alpha-form of imatinib, wherein the seed crystals are ajcutes before imatinib mesylate started to precipitate in solution. The present invention also provides crystals of imatinib mesylate stable, free-flowing, substantially pure alpha-form, and a pharmaceutical composition containing the crystals of imatinib mesylate stable, non agglomerants.L'invention finds application in particular in pharmaceuticals.