The rheological properties in synthesis process of ultrafine а-FeOOH particle were inves tigated with RFS-Ⅱand concentric bob and cup measuring system.The results indicated that the rheological properties of the reaction slurry were mainly determined by formation mechanism and morphology of goethite.The reaction slurry was Newtonian liquid with low viscosity at the initial stage of goethite synthesis process

and was psuedoplastic fluid which fits power law at the middle-later stage.Thit slurry showed strong shear-thinning characteristic without thixtropy.The rheological properties were affect ed by reacion temperature

gas flow rate and stirring rate etc.which affected the formation process and particle morphology.The viscosity of the reaction slurry decreased strongly with doping NaSiO_3 in the synthesis system.