Magnetic fluids have been widely implemented in engineering and biomedical applications due to their tuneable rheology and magnetization. In this paper, magnetite (Fe3O4) dispersed in hexane are investigated. Synthesized by the reduction of ferric acetylacetonate, nanoparticles including nanocubes are obtained with the average size of 13.7 nm. Their dispersion only slightly modifies the wettability and viscosity of hexane. By contrast, the viscosity of the magnetic fluid is significantly increased from 0.284 to 0.339 cP when the U-tube viscometer was subjected to 142 Oe magnetic field from an electromagnet. This magnetoviscosity is attributed to the interaction between nanoparticles in response to the applied magnetic field. The adjustment of fluid flow by magnetic field can be utilized in nanolubrication and bearing.