Abstract: A device for protecting bearings of idle pulleys in belt drives includes a cover 22 having a circumferential connecting portion 23 operatively engageable with a terminal edge 13a of a fastening collar 13 positioned on the pulley and housing the bearing 18 inside. Elastic tongues 26 projecting from the cover 22 are provided at their ends with corresponding hooking teeth 24 able to engage into corresponding through engaging openings 25 in a disc-shaped flange 14, which interconnects the fastening collar 13 with a cylindrical rolling portion 13 of the pulley. The tongues 26 are elastically deformable by virtue of centrifugal force so that the interference between the hooking teeth 24 and the interconnecting flange 14 is increased by increasing the rotation speed of the pulley 2.