Abstract: Wheat straw fiber-polypropylene ( PP) composites were prepared by means of the extrusion and moulded pressing process. The effects of the wheat straw fiber content, fiber size, MAPP concentration, and temperature on the melt rheological properties of PP composites were investigated. Adding wheat straw fiber to polymer matrix can increase the melt viscosity of the PP composites. The introduction of MAPP to the system increases the flow behavior of polymer and decreases the melt viscosity. The longer the wheat straw fibers, the lower the melt viscosity, and the finer the wheat straw fibers, the higher the melt viscosity. The melt viscosity of the PP composites decreases with increasing temperature f rom 170 ℃ to 190 ℃, and increasing shear rate from 0. 01 to 0. 1 s ^-1.