Abstract: A toothed belt is described, comprising resistant inserts that each have a total diameter, indicated by ?tot, in the range between 0.9 and 3 mm. The resistant insert consist of a core consisting of at least one yarn of fibres of a first material having a diameter ?c and a number N of cover yarns of fibres of a second material. The number of cover yarns N is in the range between 10 and 25 and the N yarns entirely surround the core, moreover the ratios between the total diameter of the resistant insert and the core diameter are in the range 0.4<K<1, where K=?tot/2?(?tot??c)/4.