Titanium oxide (TiO₂) has received growing attention in photocatalyst is owing to its chemical stability and ecofriendly nature. Among the different phases of TiO₂, pure anatase and mixed-phase TiO₂ (Degussa P25) have been recognized as superior photocatalysts. Indeed, the mechanism of photocatalysis and the roles of various parameters in the process have been well documented for pure anatase TiO₂ and Degussa P25. However, the pure rutile phase remains unexplored in the context of photocatalytic applications. Thus, herein, we report a one-pot method to modify the surface of pure rutile TiO₂ and examine the factors that affect its photocatalytic performance. This modification was achieved by treating rutile TiO₂ with H₂O₂ under microwave irradiation, which led to the formation of core-shell rutile TiO₂ with a crystalline core and an amorphous shell bearing Ti³⁺ and Ti–OH species on the surface. The photocatalytic performance of this modified TiO₂ species was enhanced threefold compared with that of unmodified rutile TiO₂. This basic understanding of how to improve the photocatalytic performance of rutile phase TiO₂ will play a crucial role in enhancing the catalytic performance of other metal oxides.