Abstract: A collapsible bicycle trailer includes a rigid chassis frame, hinged side rails, a side rail locking bar, a hinged tongue, and quick release wheels. The chassis frame has a generally rectangular-shaped outer frame member, and inner frame members spaced inwardly from and parallel to, the sides of the outer frame member, with wheels rotating between the outer and inner frame members. On each side of the chassis frame are positioned a pair of side rail hinge members to which are attached the lower ends of the side rails which rotate between an extended, vertical position and a folded horizontal position. The side rail hinge members also are designed to provide the connecting means between the outer and inner frame members. A side rail locking bar is pivotally attached to the top of one side rail and unfolds to securely connect to the top of the other side rail, forming a roll bar assembly.