We calculated the composition at liquid/liquid interface when surfactant A moved from one bulk phase to another. The surfactant was able to react with chemical species M in the latter bulk phase to produce surfactant B. The homogeneous distribution of A and B at the interface was in spinodal regime, and spinodal decomposition could occur. A-rich domain formed by the spinodal decomposition could react with M, while B molecules were desorbed to a bulk phase cooperatively. We described the kinetic process by time-dependent Ginzburg-Landau equation taking into account the interfacial reaction and cooperative desorption. Calculated time-dependency of interfacial composition exhibited the oscillation which was compared with the oscillation of interfacial tension observed experimentally. Some statistical properties of the both oscillation patterns were similar to each other.