Time-resolved broad-band CCD photometry of Trans-Neptunian Object 50000 Quaoar carried out using the 1.5 m telescope at Sierra Nevada Observatory is presented. The lightcurve reveals short-term variability due to rotation of the body. The periodogram analysis shows a peak at 8.8394 +/- 0.0002 h with a confidence level above 99.9%. The lightcurve seems to be double-peaked, and therefore the rotation period would be 17.6788 +/- 0.0004 h. The amplitude of the oscillation is 0.133 +/- 0.028 mag. Under the assumption that the rotational variation is induced by an irregular shape, the minimum axial ratio of Quaoar would then be 1.133 +/- 0.028.