Abstract: An auxiliary seat for bicycles of elongated, generally cylindrical shape and having a slot running lengthwise of the seat body. The slot opens at its lower end through the material of the body and has a closed upper end, within the interior of the seat body. The auxiliary seat is mounted on the horizontal bar of a bicycle by simply slipping the slot over the bar until the closed upper end of the slot is brought into firm, embracing engagement with the bicycle bar. No special tools, brackets, or hardware are required for installation or removal of the auxiliary seat. The seat is mounted on the horizontal bar of a bicycle, forwardly of the main seat for secure and safe support of a passenger, such as a child.