The present invention relates to a levelling system for motor vehicles which allows the shaft (X) that hinges a truck body (20) or other loading surface (20') defining a loading structure, to an auxiliary frame (2) defining, or forming part of, the vehicle's supporting structure, to remain horizontal so as to enable the body (20) or loading surface (20') to be used effectively; the levelling system basically includes means (4) for detecting the inclination of the hinge shaft (X) to the horizontal (Z) and means (5) for adjusting the inclination consisting of a bracket or lever (51) placed between the supporting structure and the loading structure, pivoted to a second shaft (Y) and operated on by at least two variable extension elements (52s, 52d) connected to the supporting structure and designed to vary the inclination of the latter in accordance with the readings of the detecting means (4).