Cycloidal speed reducers belong to the new generation of mechanical gears. Cycloidal speed reducers are increasingly used in modern engineering due to their good performances. Friction exists at all points of contact between the moving elements of cycloidal speed reducers, as one of the main causes of power losses in power transmission, in this paper, the friction of the contact of cycloid disc and housing rollers has been taken into account, while the friction at the contact of cycloid disc and output rollers, and at the contact of cycloid disc and central roller bearings are neglected. The effect of friction on the distribution of contact force, the friction torque value is analysed as well as efficiency. This paper presents 2 analytical models for calculating the values of contact force and friction torque. The 2nd model opposed to the 1st, taking into account the phenomenon of friction. The results. showed that friction significantly affects the distribution of normal force. Increase of the friction produces the contact forces and friction torque increase, also, while efficiency is decreasing.