Strain rate and shear viscosity are measured for Zn-Al eutectoid alloy under continuous heating rate conditions.The minimum values of the shear viscosity accompanied by the eutectoid change process have been observed.The stress dependence of the strain rate and the heating rate dependence of minimum values of the shear viscosity have been investigated.It is found that the relation between strain rate and the stress in the temperature region of the phase transformation obeys Newtonian viscous flow law.The viscous flow behaviour of Zn-Al eutectoid alloy in the temperature region of phase transformation can be explained with the number and the property of the phase interface.Comparing the activation energy of the phase transformation with that of viscous flow of the phase interface,it is found that the fluidity of phase interface is likely to be a primary factor which influences phase transformation process.In a previous work,the minimum values of viscosity have been observed in glass transition and crystallization process of amorphous Pd-Cu-Si alloy.According to these results,it is shown that the minimum viscosity emerged in structural transition process has some universality.