Viscosity of settling suspensions was studied experimentally in a series of reduced gravity parabolic flights aboard NASA's KC-135 aircraft. Slurries were made using silica sand (0.150 mm < d(p) < 0.212 mm) and glycerol solution. The experimental set-up incorporated instrumentation to measure the apparent viscosity of the sand suspensions at the wide range of the shear rates. The container had transparent walls to allow visualization of the structure changes involved in Couette flow in reduced gravity. Experiments were performed over a broad range of gravitational accelerations including microgravity and double gravity conditions. The results of the flight and ground experiments reveal significant differences in the apparent viscosity of sand suspensions and overall void factor in microgravity as compared to l-G conditions.