The hot deformation behavior of Mg-5Y-0.5Ce-0.5Zr magnesium alloy was studied by means of hot compression tests at deformation temperatures from 300 oC to 450 oC and strain rates from 0.01 s-1 to 1 s-1. The results showed that the flow stress of the alloy is changed with deformation temperature and strain rate during the hot compression deformation. The flow stress of the alloy decreases with increasing deformation temperature at the same strain rate, and decreases with decreasing strain rate at the same deformation temperature. The constitutive equation for hot compression flow stress of the alloy is established in a hyperbolic-sine form. The hot deformation activation energy Q of the alloy is 253 kJ/mol.