Preparing a freeze-dried composition containing bendamustine or its salt, comprises: (a) freezing a solution containing bendamustine or its salt in a first freezing temperature; (b) optionally, annealing the frozen solution at -25[deg] C to -10[deg] C and freezing at a second freezing temperature i.e. lower than first freezing temperature; and (c) drying the frozen solution of step (a) or (b) at a first drying temperature of -5[deg] C to 5[deg] C for at least 10 hours, to produce a freeze-dried composition. An independent claim is also included for the freeze-dried composition comprising bendamustine or its salt. ACTIVITY : Cytostatic. MECHANISM OF ACTION : None given.