In this article, a study was presented on the adsorption activity of a new nanocomposite particle Fe3O4@1, which was synthesized by combining [Cu(HL)2]2H2[P2Mo5O23]·10H2O (1) (HL = 2-acetylpyridine semicarbazone) and Fe3O4 nanoparticles. Transmission electron microscopy and X-ray powder diffraction analyses revealed that Fe3O4@1 possessed high crystallinity with an average particle size of 19.1 nm. The adsorption activity of the as-prepared Fe3O4@1 was investigated by photometrically monitoring the removal of methylene blue, rhodamine B, safranine T, gentian violet, fuchsin basic, and methyl orange from aqueous solutions. Significantly, we could easily separate Fe3O4@1 from the reaction media by applying an external magnet. Furthermore, the recycling performance was observed using methylene blue, revealing the recyclability and high stability of Fe3O4@1. It was shown that Fe3O4@1 is a promising candidate material for adsorbing cationic dyes in aqueous media.