A unit for sterilizing strip packaging material for a pourable food product packaging machine, and having a sterilizing chamber for containing a liquid sterilizing agent and along which the packaging material is fed; a control circuit for controlling the sterilizing agent, and in turn having a collecting tank, input means for feeding the sterilizing agent from the tank to the chamber, and a drain assembly for draining the sterilizing agent from the chamber into the tank; a control system for controlling the temperature in the chamber; and preheating system for preheating the sterilizing agent in the tank, and which may be activated prior to feeding the sterilizing agent from the tank into the chamber; the preheating system for preheating the sterilizing agent may be activated independently of the control system for controlling the temperature in the chamber to bring the sterilizing agent to a temperature at least equal to that of the chamber before the sterilizing agent is fed into the chamber.