A clamping device for a bicycle carry rack, comprising: a tube, a first clamp unit, a second clamp unit and a fastening unit, the first clamp unit and the second clamp unit respectively located on two ends of the tube, an end member connected to one end of the tube; the fastening unit having a pin which includes a head and a threaded end respective formed on two ends thereof, the pin extending through the first clamp unit, the tube, a spring, the second clamp unit and threadedly connected to a knob by the threaded end, the spring connected to the second clamp unit, the fastening unit connected between the first and second clamp units (10, 20), and the first clamp unit being a C-shaped unit and including a clamping slot and an entrance which communicates with the clamping slot, a notch defined in the first clamp unit and communicating with the entrance, the clamping slot of the first clamp unit adapted to clamp a frame of a bicycle carry rack via the entrance, a pivotal portion formed in the first clamp unit and transversely located below the clamping slot, the first clamp unit being pivotable about the pivotal portion, a receiving groove defined in the first clamping unit, a contact portion formed between the clamping slot and the receiving groove, a restriction recess defined in the first clamp unit and located opposite to the receiving groove, and the head removably located in the restriction recess, the clamping device being characterized in that the spring is separated from the end member by clamping the second clamp unit, and the tube travels a distance so that the head on the pin is separated from the restriction recess, the first clamp unit is pivoted and the contact portion contacts the tube, the clamping slot is adapted to clamp the frame of the bicycle carry rack via the entrance, and the pin is engaged with the notch, the second clamp unit is released to force the head on the pin to be engaged with the restriction recess. a tube, a first clamp unit, a second clamp unit and a fastening unit, the first clamp unit and the second clamp unit respectively located on two ends of the tube, an end member connected to one end of the tube; the fastening unit having a pin which includes a head and a threaded end respective formed on two ends thereof, the pin extending through the first clamp unit, the tube, a spring, the second clamp unit and threadedly connected to a knob by the threaded end, the spring connected to the second clamp unit, the fastening unit connected between the first and second clamp units (10, 20), and the first clamp unit being a C-shaped unit and including a clamping slot and an entrance which communicates with the clamping slot, a notch defined in the first clamp unit and communicating with the entrance, the clamping slot of the first clamp unit adapted to clamp a frame of a bicycle carry rack via the entrance, a pivotal portion formed in the first clamp unit and transversely located below the clamping slot, the first clamp unit being pivotable about the pivotal portion, a receiving groove defined in the first clamping unit, a contact portion formed between the clamping slot and the receiving groove, a restriction recess defined in the first clamp unit and located opposite to the receiving groove, and the head removably located in the restriction recess, the clamping device being characterized in that the spring is separated from the end member by clamping the second clamp unit, and the tube travels a distance so that the head on the pin is separated from the restriction recess, the first clamp unit is pivoted and the contact portion contacts the tube, the clamping slot is adapted to clamp the frame of the bicycle carry rack via the entrance, and the pin is engaged with the notch, the second clamp unit is released to force the head on the pin to be engaged with the restriction recess.