The hot deformation behavior of ZK60 and ZK60(0.9Y) magnesium alloys was investigated by hot compressive tests on Gleeble-1500 thermal simulation test machine in temperature range from 473 to 723 K and strain rate from 0.001 to 1s-1. The stress exponent and the deformation activation energy were calculated. The constitutive equation of the plastic deformation of ZK60 alloy was obtained by introducing Zener-Hollomon parameter. The results show that the true stress-strain curves of the alloys have dynamic recrystallization character under the present deformation conditions; within the temperature range from 573 to 723 K, the stress exponent increases with the increase of deformation temperature and the increment increases gradually. The deformation activation energy changes with the deformation temperature and strain rate. Compared with the ZK60 alloy, the deformation activation energy of the ZK60(0.9Y) alloy decreases by 30% and the materials constant (n and A) also decrease.