Reduced graphene oxide (RGO) was respectively modified with tin dioxide (SnO₂) and titanium dioxide (TiO₂) via a direct redox reaction between the graphene oxide (GO) and the reactive cations Sn²⁺ and Ti³⁺, forming RGO–SnO₂ and RGO–TiO₂ composites. During this redox reaction, GO was reduced to RGO while Sn²⁺ and Ti³⁺ were oxidized to SnO₂ and TiO₂, depositing on the surface of the RGO. The composite materials were found to exhibit very interesting photocatalytic properties for degrading Rhodamine B under visible light irradiation. First, their photocatalytic activities were higher than that of P25 (a commercial TiO₂ as a benchmark photocatalyst). Second, the reaction mechanism catalyzed by the composite materials was different from that of semiconductor photocatalysis. Characterization data showed that the excellent photocatalytic performance of the composite materials was associated with the good electrical conductivity and effective charge separation because of the presence of RGO. The present work opens up a new avenue to preparing RGO-based composite materials and provides new insights into the photocatalytic degradation of dyes under visible light irradiation.