Frictional behaviour of magnesium alloy AZ31B (Mg-3%Al-1%Zn) is measured with the tapered plug penetration test under dry condition. The cemented tungsten carbide (WC) plugs are coated with diamond like carbon (DLC), TiA1N. The cylindrical hollow billets of AZ31B heated to the temperature of 200℃ are penetrated by the tapered plugs. DLC coating is effective in prevent AZ31B from adhering to the tool surface. To examine the deformation behaviour of the billet during the plug penetration test, the finite element simulation is carried out. From the simulation and experimental results, the coefficient of friction of AZ31B is estimated.