A compact trailer (1) comprising a connecting element (13) that can be associated with a frame of a bicycle or motorcycle, and a cart (2) that has a loading bed (3) and an edge provided with at least two mutually opposite side walls (6) with which respective wheels (7) for moving the trailer resting on the ground (S) are associated so that they can rotate about respective axes that are transverse to the direction of advancement (A) of the trailer (1). A recessed cavity (8) is provided on each one of the two side walls (6) and at least partially accommodates the respective wheel (7). Each cavity (8) has a depth that is at least equal to the axial space occupation of the respective wheel (7) accommodated inside it, so that in plan view the wheels (7) do not protrude from the outline of the cart (2).