Significant amount of plutonium have been discharged and accumulated from the conventional LWRs and CANDU reactors. Reducing this reactor grade (RG) plutonium is very important because it may be misused and/or released accidentally into the environment. Fusion-fission (hybrid) reactors have strong potential on burning plutonium effectively. This study presents the burning of RG plutonium mixed with thorium in a hybrid reactor for an operation period of 24 months. The effect of various fuel mixtures (98% ThO2 + 2% RG-PuO2, 94% ThO2 + 6% RG-PuO2 and 90% ThO2 + 10% RG-PuO2) and coolants (Flinabe, natural lithium and Li20Sn80) on the reactor's performance was investigated. Numerical results showed that utilization of RG plutonium in the mixed fuel in such a hybrid reactor not only enhanced the reactor's performance but also reduced its Pu-239 content significantly.