The aim of this paper is the study of rheological behaviour of the recycled organic sand (ROS) in cement mortar, using derived sand from recycled asphalt pavement (RAP). Four substitutions amount of ROS sands (25%, 50%, 75%, and 100%) against the weight of natural sand (NS) were used to obtain M 25, M 50, M 75, and M 100 respectively which were compared with the reference mortar M 0. In this study, the water/cement (w/c) ratio was kept constant at 0.55 for all mixtures. Fresh properties were given form slump test and spread measurements, when, the rheological parameters such as shear stress, yield stress and plastic viscosity were obtained by using a rotating Anton Paar rheometer; the test result shows that both of slump and spread were negatively affected by increasing the sand substitution. The shear stress, yield stress and plastic viscosity were increased with the increasing the substitution amount. All mortars followed the Bingham model until 50% of ROS substitution, after this amount, the obtained mortars were segregated.