In this article, titanate and zinc stearate modified superfine magnesium hydroxide [Mg(OH)(2)] was filled into polypropylene (PP) as a flame retardant (FR). The structure and morphologies of untreated and treated Mg(OH)(2) particles were characterized by Fourier transform infrared (FTIR), wide-angle X-ray diffraction (WAXD), and scanning electron microscope (SEM). PP/Mg(OH)(2) (1:1) composites were also prepared in co-rotating twin-screw extruder, and the effects of treatment agents on the rheological behavior, mechanical properties, and flame retardancy of PP/Mg(OH)(2) composites were studied. The results from FTIR and WAXD show that treatment agents are adsorbed onto the surface of Mg(OH)(2) particles. The complex viscosity (eta*) values of the composites decrease with the addition of various treatment agents. Surface treatment agent could significantly improve tensile and impact strength of PP/Mg(OH)(2) composites due to its enhanced interfacial adhesion between Mg(OH)(2) particles and the PP matrix. According to limiting oxygen index (LOI), titanate treated magnesium hydroxide (MH) greatly enhanced flame retardancy of PP/Mg(OH)(2) composites.