A belt tensioner for a belt drive of a motor vehicle engine, comprising: a fixed part configured to be fixed with respect to the engine and provided with a pivot defining a rotation axis; an arm having a connection portion hinged to the pivot and rotatable about the rotation axis and an opposite portion rotatably supporting a pulley configured to cooperate with a belt of the drive; a main spring interposed between the fixed part and the arm to exert thrust on the arm such as to rotate said arm towards the belt; and at least one rolling bearing interposed between the arm and the pivot to support the arm and ensure the alignment thereof.