Abstract: A modular tube assembly includes first and second upright tubes and at least one connecting rod unit. The at least one connecting rod unit includes a connecting rod and at least one spring-loaded pin. The connecting rod interconnects the first and second upright tubes, and has a first end corresponding in position to at least one engaging hole of the first upright tube, and a second end corresponding in position to at least one engaging hole of the second upright tube. The at least one spring-loaded pin has a securing portion secured to one of the first and second ends of the connecting rod, and a movable portion movable resiliently relative to the securing portion and engaging removably the at least one engaging hole of a respective one of the first and second upright tubes.