Transient viscosity growth measurements at the startup of shear flow were performed on long glass fiber-filled polypropylene. Samples were prepared with fibers pre-oriented either in 1-direction, 3-direction or random in 1-3 plane, where the 1-direction is the direction of shear motion, the 2-direction is perpendicular to the shear plane and the 3-direction is the neutral direction. A sliding plate rheometer incorporating a shear stress transducer was constructed in the lab. It was shown that this device works well for the tested materials including a Newtonian oil, a low density polyethylene (LDPE) and short glass fiber-filled polypropylene. The transient viscosity growth behavior for long glass fiber suspensions was subsequently investigated. The results suggested that both, fiber length and fiber concentration have pronounced effect on the steady state suspension viscosity. It was also observed that the transient behavior of the pre-oriented samples was highly dependent on the initial orientation state of the fibers.