Monodispersed, homogeneous core–shell Ta_xO@Ta₂O₅ (x = 1, 2) composite nanoparticles (NPs) are successfully synthesized via one-step liquid phase laser ablation (LPLA) of a tantalum metal plate in ethanol. The morphology, phase structure, and surface states of the core–shell NPs are investigated by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The LPLA-derived spherical-like NPs consist of well-crystallized Ta_xO cores with diameters of 10–40 nm and amorphous-like Ta₂O₅ shells with a thickness of ca. 5 nm. A possible formation pathway for Ta_xO@Ta₂O₅ core–shell NPs is proposed on the basis of LPLA and subsequent reactive quenching processes. Photocatalytic degradation of methylene blue in the liquid phase serves as a probe reaction to evaluate the activity of the as-prepared core–shell NPs under the irradiation of UV light. Theoretical calculation based on density functional theory indicated the metallic nature of the core TaO phase. Interestingly, compared with pure Ta₂O₅ powders, the incorporation of suboxide Ta_xO cores into the shell of Ta₂O₅ contributes to an enhancement in photocatalytic activity. This work provides new information that may be used for the design and novel application of homogeneous core–shell nanostructures.