•Analytical efficiency model considering power losses in meshing and bearings.•Convergence of the results obtained by calculations and by testing the prototype.•High efficiency of the transmission at nominal load (90–96%).•Power loses in rolling bearings are several times greater than in meshing. The aim of the article is to investigate the efficiency of the novel eccentric rolling transmission, which is a simplification of the cycloidal reducer, with parallel but not overlapping shaft axes. In this paper, a kinematic and load distribution analysis are presented with a view to determining the forces and rotational speeds necessary for efficiency calculation. The developed efficiency model involved power losses in rolling bearings, at meshing, as well as churning and windage power losses. For the verification, a transmission prototype with a 10:1 gear ratio and a dedicated test stand were designed and built. The results of the research showed that most substantial power losses occurred in the bearings and were several times greater than the losses associated with friction between the active surfaces of its main components. The transmission efficiency improved with increasing load and decreased with increasing rotational speed, reaching a maximum of 96% at nominal torque. The proposed model allows predicting the efficiency of the transmission at the stage of its design, which can further facilitate the optimization of the transmission parameters considering expected operational conditions.