With the full tailings of an ore as research object, the rheological parameters of the filling slurry with different concentrations and cement-sand ratios were measured by MCR52 rheometer, and the extensibility of slurry was also measured. Mass concentration of slurry has a largest impact on the rheological properties of slurry, followed by cement-sand ratio. At given mass concentration, the yield stress and average viscosity of slurry both declined whereas extensibility increased with the reduction of cementitious material content. At given cement-sand ratio, the yield stress and average viscosity enhanced whereas extensibility weakened with the increase of mass concentration. With the filling slurry concentration increasing from 76% to 78%, the yield stress and the average viscosity surged by two to three times and the extensibility abated sharply, which suggest that filling slurry of low concentration is of better fluidity. The filling slurry of full tailings has obvious characteristics of “shear thinning”. The fluidity of slurry can be directly characterized by extensibility.