In this study, an experimental investigation on the synthesis method of a ferro-fluid was conducted in order to obtain a highly stable ferro-fluid. For this purpose, various surfactants are applied for colloidal stabilization among which tetra methyl ammonium hydroxide (TMAOH) showed the best performance. Several methods of characterization were chosen to characterize synthesized ferro-fluids such as Zeta potential and the particle size analysis by Dynamic Light Scattering (DLS). Based on the DLS results, the average diameter of Fe3O4 nano-particles was about 30 nm. Besides, the Zeta potential analysis was applied to investigate the stability of synthesized ferro-fluids. Moreover, the dynamic viscosity of the ferro-fluid is estimated at four different temperatures (20 oC, 35 oC, 50 oC, 65 oC). Based on the results, the ferro-fluid viscosity is decreased significantly by the temperature increase. Further, it is obvious that the viscosity of the ferro-fluid is decreased exponentially in terms of shear rate which determines its shear thinning (non-Newtonian) behavior. پرونده مقاله