Nowadays, the energy crisis has caused widespread concern about sustainable energy. Solar energy, as a sustainable, renewable energy, has attracted the attention of many researchers. Compared with other solar energy utilization, solar collectors are more efficient and commercial devices to collect solar energy. In the present study, well dispersed magnetic nanofluids (MNFs) are reported and exhibit the excellent optical thermal conversion performance under the suitable magnetic intensity and direction. In this work, the colloidal stability of MNF was improved via forming particle – micelle complexes in which the magnetic nanoparticles were captured within the micelle of surfactant. A surface modification of oleic acid was carried out to enhance the interaction between the particle and surfactant. The hydrodynamic diameter was found to be very close to the real size of particle. Meanwhile, a highly efficient solar collection system was built based on controlling the optical thermal performance of MNF by magnetic fields. The test results show that using MNF as a heat transfer fluid increases the efficiency of solar collectors. The collection efficiency of MNFs is much higher than that of water even though the particle concentration is only 0.05 vol %. In the presence of the external magnetic field, the solar collector efficiency increases to the maximum, 25% higher than the conventional parabolic trough and 12% higher than the selective surface absorber. The study indicates that MNFs, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies. All these studies show the potential of MNFs in solar thermal conversion applications.