A telescopic arm for a lift truck, of a type having at least one external arm (2) and at least one extending arm (3) which extending arm (3) is slidably inserted along a longitudinal axis (x) thereof internally of the external arm (2). The external arm (2) and the extending arm (3) have box sections, in which a lower part (4) exhibits at least two tracts (5), symmetrically arranged with respect to a vertical plane of symmetry (π), which delimit a concavity facing inwardly of the section and which at least two tracts (5) are inclined by a determined angle of inclination (α) with respect to the plane of symmetry (π).