This experimental study is conducted to explore the rheological behavior of magnetite-water ferrofluid in the attendance of an external magnetic field (MF). Tetramethylammonium hydroxide is used as surfactant to increase the stability of prepared ferrofluids. The impacts of MF strength (0–480 G) and volume concentration of nanoparticles (0.3–1.5%) on the outcomes are examined. It was found that as the shear rate increases, the viscosity decreases sharply and then tends to a fixed number and therefore, the magnetite-water has non-Newtonian pseudoplastic behavior. It was also found that the application of the MF both increases the viscosity and enhances the non-Newtonian behavior of the ferrofluid. Moreover, it was found that the rise of nanoparticle concentration (φ) leads to the increase of ferrofluid viscosity. Then, the artificial neural network is applied to develop a prediction model for the rheological behavior …