Knowledge about rheological properties of biomass is necessary for optimization of pelleting process as well as the design of devices with optimum energy and pressure to determine the effect of different variables on the density and durability of produced pellets. Therefore, in this study a shear vane was used to determine the rheological properties of biomass materials and some rheological properties of cow manure. The experiments were done at moisture content levels of 35, 40 and 45% (w.b.), and rotational speed of the shear vane test chamber in three levels of 0.1, 0.2 and 0.3 rpm. The analysis of variance of moisture content and rotational speed of the chamber on the measured traits using SAS software showed that the rotational speed has no significant effect on none of the traits at 1% level. The independent effect of moisture content was significant on all the traits. The interaction between moisture content and rotational speed of the chamber was not significant on any of the traits. The highest maximum torque, maximum shear stress and maximum yield stress were achieved at 35% moisture content and rotational speed of 0.1 rpm. The lowest maximum torque, minimum shear stress and minimum yield stress was found at 40% moisture content and rotational speed of 0.1 rpm.