This invention discloses a novel stable crystal form of imatinib mesylate,designated by us as .alpha.2 Form, which is stable at room temperature andeven at higher temperatures upto 120 ~C and accelerated stress conditions and,freely soluble in water. This invention also discloses a pharmaceuticalcomposition containing the novel stable .alpha.2 form of Imatinib mesylate andother usually employed excipients, useful in the treatment of ChronicMyelogenous Leukemia (CML). This new .alpha.2 Form of imatinib mesylate isprepared by slurrying Imatinib base in isopropanol at room temperaturefollowed by addition of methane sulfonic acid and maintaining 50-60 ~Cfollowed by filtration. This invention also discloses another process for thepreparation of the novel, stable .alpha.2 crystalline form of ImatinibMesylate by the conversion of Imatinib mesylate .beta.-polymorphicmodification by suspending it in water and organic solvents, distilling offwater azeotropically, cooling and filtering to obtain the .alpha.2 crystalform.
