Abstract : The neutrino telescopes have important discovery potentials in astrophysics, neutrino physics and dark matter searches. A proposal for the construction of such a telescope in the Mediterranean Sea was made in April 1999 by the ANTARES collaboration. The low energy performance (tens of GeV - 300 GeV) of the proposed detector is characterised. The resolution on the neutrino zenith angle is about 5° for 20 GeV neutrinos and improves to 3° between 160 and 300 GeV. The detector effective volume varies between 8.10^5 m3 at 20 GeV and 2,5.10^6 m3 between 160 and 300 GeV. An energy resolution better than 30% is obtained for muons with energies higher than 20 GeV, for neutrinos interacting in the detector volume. The detector is therefore well suited for the study of atmospheric neutrino oscillations. With 3 years of data taking, ANTARES can measure the oscillation parameters with a precision better than 33% (better than the SuperKamiokande precision) for a large region of the parameter space.