VHE Spectral Properties of Mrk 501 with the CAT telescope

We report here observations of the active galactic nucleus Mrk 501, at energies above 250 GeV carried out with the CAT atmospheric imaging telescope from March 1997 to Autumn 1998. This source was in a high state of activity at several different wavelengths in 1997, and the observed flux at TeV energies has been seen to change by a factor of ~ 20 from from 1995 and 1996 fluxes. CAT observations also indicate a curved spectrum at TeV energies, and a correlation between the gamma-ray intensity and the spectral hardness. The temporal variability and the TeV spectral properties are examined.