Abstract: The effect of magnetic field and temperature on the viscosity of magnetic fluid was studied.The viscosity was reduced with increasing temperature.When the temperature of the surroundings was kept constant,the viscosity of magnetic fluid increased with increasing the magnetic field.This change was related to the magnetic intensity and acting time.When the acting time was increased to a certain value,the viscosity tended to a constant value.If the applied field was kept constant,the viscosity tended to be steady with increasing time.When the magnetic field was increased to a certain value,the viscosity tended to a constant value.