We describe synthesis of three kinds of phosphonium-presenting superparamagnetic iron oxides (SPIOs) with different anchoring motifs and their stimuli responsiveness to anion exchange. The series of the modified SPIOs with or without direct bonding to phosphonium bromides were prepared. With these modified SPIOs, an influence of the anion exchange on the dispersion states was investigated. Accordingly, the direct anchoring of phosphonium cation to the surface could contribute to improving sensitivity of the aggregation formation when the hydrophobicity of the surface was enhanced. Finally, it was found that the modified SPIOs with directlyconnected phosphonium cation immediately formed the assembly in the presence of citrate anion.