Surfactant‐free α‐Fe 2 O 3 nanorings (NRs) were directly converted into water‐dispersible Fe 3 O 4 NRs through a simple and straightforward approach. In this process, uniform α‐Fe 2 O 3 NRs obtained through hydrothermal synthesis method are firstly thermally reduced to hydrophobic Fe 3 O 4 NRs in the presence of hydrophobic oleic acid surfactant and non‐polar trioctylamine solvent (under a flow of 5% H 2 /95% Ar). Subsequently, oxidative cleavage of oleic acid capping agent using sodium periodate oxidising agent is imparted to yield water‐dispersible Fe 3 O 4 NRs. As compared with the traditional solid‐state reduction in tube furnace, the obtained Fe 3 O 4 NRs using solution‐based reduction process can retain its original uniform ring shape with good crystallinity and well‐defined magnetic vortex domain. Moreover, with the presence of azelaic acid on the surface of hydrophilic Fe 3 O 4 NRs, antibody or drugs can be easily conjugated, which further boost its potential theranostics application. This work provides a convenient approach to convert surfactant‐free nanoparticle (NP) powders into water‐dispersible NPs colloidal solutions for various biomedical applications.