We study the possibility for directly measuring the polarized gluon distribution in the process gamma p -> (t) over bart. It is shown that polarization asymmetry of the final top quarks is proportional to the gluon polarization. With available energy and luminosity, the collision of a polarized proton beam and a Compton backscattered photon beam call create polarized top quarks which carry the spin information of the process. Energy dependence and angular distributions of the polarization asymmetry of the top pairs has been discussed including statistical uncertainty. (C) 2009 Elsevier B.V. All rights reserved.