Recent geological observations support the subduction of some oceanic arcs into the mantle. For example, the Izu-Bonin arc is considered to be partially subducting underneath the island of Honshu, Japan, despite its lower density than that of surrounding mantle, after the vertical collision with Honshu at similar to 17Ma. Seismological surveys have clarified the internal structure of the arc, which consists of the basaltic and boninitic upper crust, the felsic middle crust, the intermediate upper-lower crust, and the mafic lower crust. This structure extends and moves northward toward Honshu. Among these components, part of the middle, the intermediate upper-lower, and the lower crust is thought to be subducting. Here in order to estimate the subduction rate of granitic materials in oceanic arcs to the deep mantle, we have conducted numerical simulations of the subduction of arcs based on the finite element method and investigated the effect of arcs' sizes and shapes and slab temperature. The results show that the subduction rate heavily depends on the geometry of the arcs or temperature profiles of the subducting slabs. When the size of the arc or the temperature of the slab is smaller, the subduction rate grows larger owing to competition between upward buoyancy and downward viscous drag from slabs. The results also show that about 20% of the felsic crust materials in oceanic arcs that are comparable in size to the Izu-Bonin arc can be subducted into the deep mantle when the temperature of the subducting slab is of the usual value.