The Okinawa Trough is different from other typical backarc spreading basins because the, acidic volcanic rock (pumice) is extensively distributed in it. Systematic mineralogical and petrochemical study on a representative core (Z14–5) to characterize the magmatic evolution of the Trough during its early spreading stage showed that the pumice magma was originally from the mantle, but underwent full crystallization differentiation and was possibly contaminated by crust-derived material. With time, the acidic volcanic activities of the Okinawa Trough have an evolutional tendency of shifting to relatively basic magma activity. With further spreading of the Trough the magmatic activity will be intensified and the crust of the Trough will develop from the transitional type to the oceanic type.