The invention relates to a shock-absorbing seat tube, including an outer tube and an inner tube sleeved within the outer tube. The inner tube is adapted for connection to a bicycle saddle from below through a joint. The seat tube is provided with a height adjustment device having a supporting end inserted into the inner tube, and a shock-absorbing device disposed in the inner tube at a position above the height adjustment device and includes a fixing part and a damper part. The fixing part passes at its top end through the inwardly protruded portion of the inner tube and is arranged in the barrel portion of the inner tube. The damper part is arranged between the inwardly protruded portion and the supporting end.