To provide a method for preventing the slip of piercer rolls by jetting a slip preventing agent to a round bar and the piercer rolls in piercing with a piercer.

In the method for preventing the slip of the piercer rolls 1, the current values of the motors for driving the piercer rolls 1 during rolling the round bar 8 are detected every moment with a sensor 4 which is provided on a piercer roll galvanometer 3. When the current value is not more than a prescribed current value from the sensor 4, the generation of the slip is predicted, a oil feeding system 5 for slip preventing agents is operated and the slip preventing agent is jetted to the piercer rolls 1 and round bar 8.